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Geological sites in the Clyde and Avon Valleys: assessment for the Shaping Our Landscape Trail Geology and Landscape Scotland Programme Commissioned Report CR/15/128


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BRITISH GEOLOGICAL SURVEY

GEOLOGY AND LANDSCAPE SCOTLAND PROGRAMME COMMISSIONED REPORT CR/15/128

Geological sites in the Clyde and Avon Valleys: assessment for the Shaping Our Landscape Trail The National Grid and other Ordnance Survey data © Crown Copyright and database rights 2015. Ordnance Survey Licence No. 100021290 EUL.

K Whitbread

Keywords Clyde Valley; Geodiversity; Geoheritage; Geological trail. Front cover Corra Linn, Falls of Clyde (© K Whitbread BGS/NERC) Bibliographical reference WHITBREAD, K. 2015. Geological sites in the Clyde and Avon Valleys: assessment for the Shaping Our Landscape Trail. British Geological Survey Commissioned Report, CR/15/128. 53pp. Copyright in materials derived from the British Geological Survey’s work is owned by the Natural Environment Research Council (NERC) and/or the authority that commissioned the work. Ownership and copyright of all outputs from this project, including all final reports, data sets and maps etc. will be jointly owned by the Clyde and Avon Valley Landscape Partnership and the Natural Environment Research Council. You may not copy or adapt this publication without first obtaining permission. Contact the BGS Intellectual Property Rights Section, British Geological Survey, Keyworth, e-mail ipr@bgs.ac.uk. You may quote extracts of a reasonable length without prior permission, provided a full acknowledgement is given of the source of the extract. Maps and diagrams in this book use topography based on Ordnance Survey mapping. © NERC 2015. All rights reserved

Keyworth, Nottingham British Geological Survey 2015


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BRITISH GEOLOGICAL SURVEY The full range of our publications is available from BGS shops at Nottingham, Edinburgh, London and Cardiff (Welsh publications only) see contact details below or shop online at www.geologyshop.com The London Information Office also maintains a reference collection of BGS publications, including maps, for consultation. We publish an annual catalogue of our maps and other publications; this catalogue is available online or from any of the BGS shops. The British Geological Survey carries out the geological survey of Great Britain and Northern Ireland (the latter as an agency service for the government of Northern Ireland), and of the surrounding continental shelf, as well as basic research projects. It also undertakes programmes of technical aid in geology in developing countries. The British Geological Survey is a component body of the Natural Environment Research Council.

British Geological Survey offices BGS Central Enquiries Desk Tel 0115 936 3143 email enquiries@bgs.ac.uk

Fax 0115 936 3276

Environmental Science Centre, Keyworth, Nottingham NG12 5GG Tel 0115 936 3241 Fax 0115 936 3488 email sales@bgs.ac.uk Murchison House, West Mains Road, Edinburgh EH9 3LA Tel 0131 667 1000 email scotsales@bgs.ac.uk

Fax 0131 668 2683

Natural History Museum, Cromwell Road, London SW7 5BD Tel 020 7589 4090 Fax 020 7584 8270 Tel 020 7942 5344/45 email bgslondon@bgs.ac.uk Columbus House, Greenmeadow Springs, Tongwynlais, Cardiff CF15 7NE Tel 029 2052 1962 Fax 029 2052 1963 Maclean Building, Crowmarsh Gifford, Wallingford OX10 8BB Tel 01491 838800 Fax 01491 692345 Geological Survey of Northern Ireland, Department of Enterprise, Trade & Investment, Dundonald House, Upper Newtownards Road, Ballymiscaw, Belfast, BT4 3SB Tel 028 9038 8462

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Website www.bgs.ac.uk Shop online at www.geologyshop.com


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Foreword This report, produced by BGS Scotland, is an assessment of geological sites in the Clyde and Avon Valley undertaken on behalf of the Clyde and Avon Valley Landscape Partnership. The geological assessment forms the first phase of a project to develop the ‘Shaping Our Landscape’ geological trail. The Trail is intended to engage both local people and visitors with the region’s environment and economic and cultural history through the geological ‘story’ of the landscape. A second phase of the project, to be undertaken by CAVLP in 2016, will develop onsite and online resources to enable the trail users to explore the geological history of the region.

Acknowledgements The work was partly funded by the Heritage Lottery-funded Clyde and Avon Valley Landscape Partnership. Thanks to Kirsten Robb and Sarah O’Sulliven at CAVLP for constructive discussions and company on several field visits. Thanks also to Martin Twiss (SNH) for discussions and assistance during field visits, and to Mike Brady (South Lanarkshire Council) and Steve Blow (Scottish Wildlife Trust) for providing useful information. Contributions from members of the public were also much appreciated, particularly for the discussions and useful information provided by Mike Browne, Graham U’ren and Andrew Hyton. Particular thanks to local residents Andy Nelson and Christine Murphy for providing information on the ‘hidden’ treasures of Sandyholm caves and Sampson’s Slingstane. Geological memoirs, papers, unpublished reports and webpages consulted during the work are listed in the bibliography with selected published articles cited within the text where appropriate. Maps and diagrams have been prepared by the author, except where stated. All photographs are copyright BGS/NERC. The report includes mapping data licensed from Ordnance Survey with permission of the Controller of Her Majesty's Stationery Office © Crown Copyright and/or database right 2014. All rights reserved.

Contents Foreword ......................................................................................................................................... i Acknowledgements ......................................................................................................................... i Contents........................................................................................................................................... i Summary ....................................................................................................................................... iii 1

Introduction ............................................................................................................................ 4 1.1 The Clyde and Avon Valley area ................................................................................... 4 1.2 Objectives and Scope...................................................................................................... 4 1.3 Community engagement ................................................................................................. 4 1.4 The Geological assessment ............................................................................................. 5 1.5 Report Outline ................................................................................................................ 6

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Regional geological perspective ............................................................................................ 6 i


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Geological history of the Clyde and Avon Valleys .............................................................. 7 3.1 The history in the rocks .................................................................................................. 8 3.2 Rivers and ice - The history in the landscape ............................................................... 14 3.3 People, rocks and landscape ......................................................................................... 22

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Shaping the trail ................................................................................................................... 23 4.1 Site Focus ..................................................................................................................... 23 4.2 Story Focus ................................................................................................................... 27

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Conclusions and recommendations .................................................................................... 28

Appendix 1 ................................................................................................................................... 29 Appendix 2 ................................................................................................................................... 47 Glossary ........................................................................................................................................ 48 Bibliography ................................................................................................................................ 49

FIGURES Figure 1 – Map of the Clyde and Avon Valley area showing the locations of geological sites ..... 5 Figure 2 – Simplified geological map of the Midland Valley of Scotland. .................................... 7 Figure 3 – Bedrock map of the CAVLP area. ................................................................................. 8 Figure 4 – Photographs of the Devonian sandstone of the Swanshaw Sandstone Formation. ....... 9 Figure 5 – Photograph of Stonebyres Quarry................................................................................ 10 Figure 6 – Photographs of Limestone Coal Formation strata in the Lower Nethan Gorge and Fiddler Burn. ........................................................................................................................... 11 Figure 7 – Underground workings in Threepwood Quarry (Sandyholm Caves). ......................... 12 Figure 8 – Photographs of Baron’s Haugh. ................................................................................... 13 Figure 9 – Superficial deposits map of the CAVLP area. ............................................................. 14 Figure 10 – Google Earth image of a section of the Greenland ice cap. ....................................... 15 Figure 11 – Map of the glacial deposits and landforms of the New Lanark and Bonnington area.16 Figure 12 – Photographs of the Falls of Clyde.............................................................................. 17 Figure 13 – The system of buried pre-glacial valleys and rock gorges along the Clyde Valley between Hamilton and Garrion Burn...................................................................................... 18 Figure 14 – Map showing the possible former course of the Mouse Water along Auchenglen ... 19 Figure 15 – Sampson’s Slingstane, near the Fiddler Burn. ........................................................... 19 Figure 16 – Sand and gravel deposits at Chatelherault.. ............................................................... 20 Figure 17 – Modern river environments of the Clyde Valley. ...................................................... 21 TABLES Table 1 – ‘Traffic Light’ summary of geological sites in the Clyde and Avon Valleys. .............. 24

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Summary In August 2015, the Clyde and Avon Valley Landscape Partnership (CAVLP), supported by the Heritage Lottery Fund and the Renewable Energy Fund managed by South Lanarkshire Council, commissioned the British Geological Survey to undertake a geological assessment of the Clyde and Avon Valley Area of Great Landscape Value. The assessment, by BGS Scotland, will provide a geological resource for the development of the ‘Shaping Our Landscape’ geological trail by CAVLP in 2016. The Trail is intended to enable people to explore the area’s geological history and its diverse links with the region’s economic, cultural and ecological heritage. The geological assessment comprised a desk study to identify geological sites and features of interest in the Clyde and Avon Valleys, followed by four days of field visits. Fifteen potential geological sites were assessed during the desk study and field survey to document their geological ‘value’, potential heritage associations and the nature of access to the site. Several of the sites visited are not recommended for access by the public. The geological history of the CAVLP area spans over 400 million years, from Devonian times through to the ongoing fluvial processes associated with the rivers Clyde and Avon today. The history of the rivers forms a strong narrative that links the ancient and modern landscapes of the area. The Devonian and Carboniferous rocks that underlie the region were formed, respectively, in vast braided river systems and dynamic deltaic settings. The area’s sandstone and coal resources, of historic importance for the economic wealth of Central Scotland, owe their origin to these ancient river systems. In the more recent geological past, since the end of the last ice age less than 20,000 years ago, it has been the erosive power of rivers that has shaped the landscape. The dramatic rock gorges on the River Clyde at the Falls of Clyde and along the River Avon, River Nethan, Mouse Water, and many minor burns, are testimony to a reconfiguring of the landscape by powerful streams charged with meltwater during and after the retreat of the ice age glaciers. The dramatic restructuring of the drainage of the Clyde has arisen from the region’s unique geographical setting in the lowlands of the Central Belt and is perhaps the best example of its kind in Scotland. Two of the key sites in the area, the World Heritage Site of New Lanark and the Falls of Clyde, and Chatelherault Country Park, provide excellent geological information in the form of visitor centre displays and geological trails. Opportunities to develop new resources for other sites could include geological guides to the Clyde and Avon Walkways and the Clyde Valley Woodlands Nature Reserves, and information panels describing the landscape history at the summit of Blackhill. The dramatic geological story of the region would lend itself to the creative use of multimedia to narrate the geological history. Interactive web-based resources utilising film, images, animation or interactive maps would help users explore the changing landscape of the Clyde and Avon Valleys over geological time, and see how the history of the area links with the wider history of Central Scotland. The web-based approach would also mean that ‘virtual sites’ could be created to tell the story of sites with high geological value, such as rock crags in the Lower Nethan Gorge, and the underground workings of ‘Sandyholm caves’, that may not be safe for public access.

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1 Introduction The Clyde and Avon Valleys, located in west central Scotland, are recognised as an Area of Great Landscape Value for the scenic characteristics of the landscape, and the diverse cultural, economic and ecological heritage of the area. The Heritage Lottery-funded Clyde and Avon Valley Landscape Partnership (CAVLP) delivers a range of projects aimed at helping communities engage with the region’s environment and rich heritage. In the summer of 2015, CAVLP instigated a project to develop the ‘Shaping Our Landscape Geological Trail’ to highlight the links between the geological history of the area, its environment and its communities. In August 2015, CAVLP commissioned the British Geological Survey to undertake the first phase of the Trail project; a geological assessment of sites within the Clyde and Avon Valley area. This report details the results of the assessment, providing information that: 1) underpins the geological ‘narrative’ for the region, 2) identifies and prioritises key sites and 3) forms a basis for planning on-site and on-line resources for users of the trail. This report supplies the information required by CAVLP to design the trail and develop associated information resources in a second phase of the project to be undertaken in 2016. The final geological trail may not include all the sites assessed in this report. 1.1

THE CLYDE AND AVON VALLEY AREA

The River Clyde flows north and west from source areas in the high ground of the Southern Uplands into the Firth of Clyde passing, along its lower course, through the city of Glasgow. The central area of the Clyde Valley, covered by the CAVLP area, includes the confluence of the River Avon with the Clyde near Hamilton, and extends upstream to the Falls of Clyde south-east of New Lanark (Figure 1). Covering 130 km2, the region includes numerous ancient woodlands, historic settlements, orchards and country estates, and has long been recognised for its scenic qualities. The area also boasts the World Heritage Site of New Lanark and the Falls of Clyde, and has a rich economic heritage of market gardening, textile production, coal mining and quarrying. The rivers themselves have long provided power; once turning the mills of New Lanark, and now producing electricity from hydroelectric power stations at Bonnington and Stonebyres. These natural resources have played an important role in the industrial development of the city of Glasgow and the economic wealth of Scotland as a whole. 1.2

OBJECTIVES AND SCOPE

The Trail is envisaged as a network of sites that are connected by a geological ‘story’ linked with a range of aspects of local heritage. Sites must be accessible by car or public transport and may include short sections of established walking trails such as the Clyde Walkway and Avon Walkway, the network of public rights of way, nature reserves, and visitor attractions including country parks, museums and information centres. The final Trail may utilise ‘traditional’ resources such as on-site information boards and leaflets, but opportunities for use of on-line resources and multi-media approaches could be explored to expand the potential for creative engagement of trail users in exploration of the region’s geological history. 1.3

COMMUNITY ENGAGEMENT

Community engagement lies at the heart of the trail project, not only at its launch and subsequent use, but also in its development. The launch of the project was accompanied by a press release inviting members of the public to provide information about sites in the area that they have 4


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visited. The press release garnered interest from the local community and members of geoconservation groups across Scotland. Several responses yielded valuable information on known sites including the Falls of Clyde, and highlighted potential ‘hidden gems’ including a large erratic boulder known as Sampson’s Slingstane, and a network of underground caverns associated with former sandstone workings.

Figure 1 – Map of the Clyde and Avon Valley area showing the locations of geological sites and places named in the text. The areas for closely spaced smaller sites have been merged for simplicity. The inset map shows the location of the area in central Scotland. 1.4

THE GEOLOGICAL ASSESSMENT

The geological assessment of potential sites for the trail comprised two phases: an initial desk study to identify sites and gather background information, and a targeted field assessment. During the desk study, geological information from published BGS geological maps and memoirs, the Geological Conservation Review series, historic maps and fieldslips, and several unpublished reports supplied by members of the public and geoconservation community, was collated. The information was used to develop a list of 15 sites for field visits. Site visits were conducted over four days in November 2015. Guidance on existing resources of geological information and the locations of known geological features of interest at the target sites were sought from nature reserve managers and rangers where possible. Following these contacts, field visits were arranged, and visits to Cartland Craigs Nature Reserve and Sandyholm 5


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Quarries were coordinated with Martin Twiss, the Scottish National Heritage Reserve Manager, and Kirsten Robb and Sarah O’Sullivan from CAVLP. During the field visits, geological sites were assessed by a walk-over reconnaissance survey. Recorded information included the locations and descriptions of key geological features and landforms, as well as general information detailing the nature and ease of access, restricting conditions, known ecological and heritage associations and any existing geological or other information resources at the site. The general descriptions of the nature of access provided here do not constitute reviews of the site safety. Some sites may require further health and safety assessments prior to inclusion in the Trail. The site information was entered into an Excel form, with locations of key features of interest recorded in ARC GIS on a tablet PC carried in the field. The individual site forms containing the information recorded in the field, along with selected photographs of features of interest are included in Appendix 1. 1.5

REPORT OUTLINE

This report provides summary descriptions of the sites visited, highlighting the main geological elements of interest, the quality of the features, and the opportunities and limitations of the sites as regards their potential for inclusion in the geological trail. A key element of the Trail is the geological narrative that develops the story of how the landscape has been shaped, and the relationship between the geological story and the history of the local communities that have lived in the area. The key objective of this report is therefore to evaluate the potential sites in terms of their significance in the context of the geological narrative. Suggestions for potential on-site and on-line information resources that could be developed to tell the story of the shaping of the landscape are also provided.

2 Regional geological perspective The Clyde and Avon Valley Area of Great Landscape Value lies within the broad tract of relatively low ground across Central Scotland that is known geologically as the Midland Valley. The Midland Valley is an ancient rift valley bound by the Highland Boundary Fault to the north and the Southern Upland Fault to the south (Figure 2). During the Devonian and Carboniferous periods (c. 410 – 310 Million years ago) Britain lay at the heart of a major continental landmass. Tensional forces on the crust at this time resulted in the formation of a series of rift basins throughout Britain as the crust extended and thinned. The Midland Valley formed as the most northerly of the rifts. The subsidence of the Midland Valley during this time created the environment for deposition of a thick succession of marine and terrestrial sediments. These sediments formed the Devonian and Carboniferous sedimentary rocks that underlie the area today and are the source of the region’s extensive coal and building stone resources. The tectonic activity also brought with it crustal melting, which resulted in the intrusion of molten rock into the newly formed sedimentary succession. The sedimentary rocks of the Midland Valley are relatively soft compared with the older, more resistant rocks of the Highlands to the north and Southern Uplands to the south. Preferential erosion of the rocks of the Midland Valley over millions of years has given rise to the relatively low-lying landscape of Scotland’s Central Belt. Within the past 2 million years, repeated episodes of glaciation have left a strong imprint on the landscape of the Clyde and Avon Valleys. During the main phases of glaciation, when ice extended across Scotland and over much of northern Britain, glaciers sourced from the western Highlands and Southern Uplands coalesced in the low ground of the Midland Valley and flowed east into the Firth of Forth. The last major glaciation of the area reached its height 20,000 – 6


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25,000 years ago. During deglaciation, the dynamic interaction of Highland and Southern Upland glaciers retreating towards the west resulted in the formation of a complex assemblage of ice marginal sediments and landforms. As the ice retreated, the drainage system of the River Clyde and its tributaries was re-established over the glaciated terrain. Glacial sediments had infilled most of the pre-existing valleys in the central area of the Clyde catchment (from Lanark to Hamilton) and powerful streams charged with glacial meltwater and outflows from glacial lakes, carved a network of new valleys deep into the glacial sediment and bedrock. The deep gorges resulting from this erosion, and the picturesque waterfalls within them, form some of the most striking geological features of the region.

Figure 2 – Simplified geological map of the Midland Valley of Scotland with timeline. Major geological faults are shown by a thick black line with a tick on the downthrown side (Source: BGS DiGMapGB data).

3 Geological history of the Clyde and Avon Valleys Sites of geological interest are distributed throughout the CAVLP area (Figure 1). The rocks, superficial deposits, and the area’s dramatic landforms are testimony to the power of rivers to shape the landscape over millions of years. In particular, the CAVLP area provides perhaps the best example in Scotland of the disruptive influence of glaciation on pre-glacial drainage systems due to its unique geographical setting. Moreover, the region and its communities continue to be shaped by the rivers today. The dynamic power of the rivers forms a strong narrative thread linking the landscapes of the past with the landscapes of the present. The following discussion of the geological history of the area, demonstrated through its geological sites, highlights the central role of rivers throughout geological history of the CAVLP area. 7


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THE HISTORY IN THE ROCKS

The Devonian to Carboniferous sedimentary rocks are dominated by sandstone, siltstone and mudstones with limestone and coal seams. Older Devonian strata are found in the Clyde Valley to the south of Hazelbank and Cartland, with younger Carboniferous strata to the north and along the Avon Valley (Figure 3).

Figure 3 – Bedrock map of the CAVLP area. Locations of sites and selected place names are also shown. Grid is British National Grid with 10 km between tick marks. 3.1.1 Devonian strata - Ancient sandy streams During early Devonian times (c. 410 - 400 Ma) the Midland Valley was a broad area of low ground bound by active faults to the south and north. Large braided channel systems flowed towards the south-west, depositing vast quantities of sand throughout the area. During this time, Scotland lay at the heart of a large continent, and was located geographically in the arid belt to the south of the equator. There were no land plants at this time, and the early Devonian rocks are dominated by fluvial sandstones and conglomerates made up of pebbles and cobbles, which formed where upland streams flowed from the high ground into the Midland Valley. The early Devonian rocks of the CAVLP area are part of the Swanshaw Sandstone Formation. The sandstone has a characteristic reddish or purplish colour where it is exposed in the gorges of the Falls of Clyde (2883, 6407) and Cleghorn Glen (2902, 6454; Figure 4). At Stonebyres Falls (2853, 6440), pebbly horizons are also seen in the sandstone beds. In places there are thin 8


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beds of mudstone or siltstone separating the thicker beds of sandstone. These finer-grained rocks have formed from mud and silt deposited in shallow ponds between the sandy channels, or on floodplains, and tend to be more erodible than the surrounding sandstone.

A

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Figure 4 – Photographs of the Devonian sandstone of the Swanshaw Sandstone Formation. (A) Sandstone exposure by the main trail near Bonnington Linn. (B) Red mudstone clasts (highlighted by blue arrows) in the base of the middle sandstone bed of the outcrop in photo A. (C) Cross-bedded sandstone exposed in the channel bed above Bonnington Linn, with Bonnington Weir in the background. (D) Cross-bedding and pebbly horizons in outcrop at Stonebyres Falls. As the fluvial sands became buried by more sediment, they were cemented and lithified to form sandstone. Whilst underground, the rocks were intruded by magma rising from deep in the Earth’s crust. The molten rock squeezed into the sandstone along planes of weakness like the planar surfaces between beds of sandstone. An igneous intrusion of relatively light coloured crystalline rock, known as felsite, forms the ridge between Blackhill (2832, 6435) and Hazelbank. Igneous rocks tend to be more resistant to erosion than the surrounding sedimentary rocks and commonly form areas of higher ground. The resistant igneous rocks also form a useful road stone, and were formerly extracted from Stonebyre Quarry (2835, 6432) on the eastern slope of Blackhill (Figure 5). In the quarry faces the felsite is split along long inclined cooling cracks forming polygonal networks of joints. These cracks formed as the hot magma contracted as it cooled and solidified, the same process that formed the famous ‘honeycomb’ network of joints at the Giants Causeway in Ireland.

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Figure 5 – Photograph of Stonebyres Quarry, view looking north. The long cooling cracks in the felsite can be seen in the face, with their columnar form seen to the right of the centre of the image. The line of pinkish rock that extends up the quarry face from the outcrop in the right foreground is a dyke intruded into the felsite. 3.1.2 Carboniferous strata – Ancient river deltas and swampy forests During early Carboniferous times (c. 360 – 310 Ma), the Midland Valley had been inundated by a shallow sea. Rivers carrying sand from the region of the North Sea formed a complex delta system. Competition between the prograding deltas and periodic rises in sea level gave rise to cyclic sequences of sediment reflecting transitions between shallow marine and terrestrial conditions. Dense, swampy, tropical forests developed on floodplains during the terrestrial periods, covering large areas of the Midland Valley. As a result, Carboniferous rocks are more varied than the older Devonian strata, comprising sandstone, siltstone and mudstone with limestones and coal seams. Carboniferous rocks underlie the area to the north and west of Hazelbank, becoming progressively younger to the north-west (Figure 3). The oldest Carboniferous strata outcrop along the Clyde valley between Crossford and Overton. The rocks were formed during the early phases of delta development and have a strong marine influence that is reflected in cyclic sequences of deltaic and shallow marine sedimentary rocks. The rocks from this period have been divided into three main units: the Lower Limestone Formation, Limestone Coal Formation and the Upper Limestone Formation (Figure 3). As the name suggests, the Limestone Coal Formation contains a number of coal seams, some of workable thickness. The unit represents a period of more terrestrial conditions during the development of the delta system, when the coals developed from vegetation accumulated in mires on the river floodplains. Rocks of the Limestone Coal Formation are exposed in the deep valley of the Fiddler Burn (2845, 6470), 0.5 km south of Braidwood, and along the River Nethan, where spoil tips and adits provide evidence of former coal workings. Although hard to access, excellent exposures of cycles of sandstone and coal-bearing mudstone occur along the Lower Nethan Gorge (2818, 6466). The vertical sandstone crags along the gorge display channel scours and cross-bedding indicative of deposition in river channels. The base of the channel sandstones also bear abundant, well-preserved fossil tree-like Lycopod branches that 10


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were carried and deposited by streams during floods (Figure 6). Mudstone units separating sandstone crags contain thin coal seams and bands of nodular ironstone that were formerly worked in the gorge. Exposures of sandstone in the Fiddler Burn show well preserved ripples indicative of former river bed surfaces, and mudstone boulders in the stream, reworked from a mine waste tip upstream, are rich in fossilised plant fragments (Figure 6).

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Figure 6 – Photographs of Limestone Coal Formation strata in the Lower Nethan Gorge and Fiddler Burn. (A) Pale-coloured sandstone crag underlain by grey mudstone in the Nethan Gorge. (B) Fossil Lycopod branches in sandstone in the Lower Nethan Gorge, oval-shaped sections and the pattern of the bark are preserved in the sandstone to the right of the image. (C) View up the bed of the Fiddler Burn. The sandstone crag to the left is undercut at the base by erosion of a mudstone bed. The channel bed contains boulders of fissile grey mudstone and pale angular sandstone derived from mine spoil tips upstream. (D) View of the eroded mudstone below the under-cut sandstone crag. The bedding plane of the sandstone below the mudstone shows preserved ripples. Strata from the mid to late Carboniferous (330 – 300 Million years) are found in the Clyde valley between Hamilton and Overton and in the Avon valley as far south as Stonehouse (Figure 3). These rocks were formed under more terrestrial conditions than those of the early Carboniferous. 11


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Throughout Central Scotland, the transition to more terrestrial conditions is marked by a belt of sandstone deposited by braided rivers that separates the limestone bearing older Carboniferous rocks from the younger formations of the Scottish Coal Measures Group. This unit of thick, cross-bedded sandstone, called the Passage Formation, crops out along the south-west side of the Clyde valley between Dalserf and Sandyholm. Passage Formation sandstone provides excellent quality building stone, formerly extracted from three quarries in the area. In Threepwood Quarry (2814, 6407), surface workings on the bed of highest quality sandstone were extended underground in a relatively extensive network of stoop and room workings excavated in the back of the small quarry (Figure 7). The workings are known locally as “Sandyholm caves” and, along with several quarries to the north, are thought to have supplied stone for the construction of Hamilton Palace.

A

B Figure 7 – Underground workings in Threepwood Quarry (Sandyholm Caves). (A) View of the entrance to the caverns worked into the back of the quarry. (B) Stoop and room workings with original wooden beam and wedges supporting the sandstone roof. The strata of the Scottish Coal Measures Group are characterised by an abundance of thick coal seams. The Scottish Lower and Middle Coal Measures formations of this group have been mined extensively for coal north of Rosebank in the Clyde Valley, and Stonehouse in the Avon Valley. The widespread extraction of coal from rocks near the surface has caused ground subsidence in some places, notably resulting in the demolition of Hamilton Palace and damage to its grand hunting lodge at Chatelherault. Subsidence related to coal mining is also responsible for the development of wetlands along the floodplain of the Clyde at Baron’s Haugh (2750, 6550;

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Figure 8). The ponds, now part of a nature reserve, are reportedly kept relatively warm in winter by inflow of water from old mine workings.

A

B Figure 8 – Photographs of Baron’s Haugh. (A) The RSPB nature reserve of Baron’s Haugh viewed from the Causeway Hide (view to the south-west). (B) Historic photograph of subsidence ponds on the Clyde floodplain in the area of Baron’s Haugh taken in 1921, view to the south-east (BGS©NERC. All Rights Reserved. 2015; archive number P002420). Notes on the image report that the river alluvium, here 22 m thick, collapsed into workings on the Ell Coal 30 m beneath the surface and flooded Home Farm Colliery (Mines Inspectors Reports, 1877, p.145) Abandoned shafts, waste tips and former mineral railways provide abundant evidence of former coal workings throughout the northern part of the CAVLP area. The route of the old mineral railway along the Avon Gorge is now a footpath in Chatelherault Country Park (2737, 6540), forming part of the geological ‘Hole Story Trail’. The excellent Chatelherault Visitor Centre provides a wealth of information on the geology and mining history of the local area.

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RIVERS AND ICE - THE HISTORY IN THE LANDSCAPE

The form of the landscape of the Clyde and Avon valleys, and the thin layer of unconsolidated superficial deposits that overly the rocks (Figure 9), reflect the complex interaction of rivers and glaciers during and after the last major glaciation of Scotland 20,000 years ago. The superficial deposits typically underlie characteristic landforms that relate to the erosional and depositional processes associated with rivers and glaciers. These include flat terraces formed in river meanders, or arcuate ridges of moraine that form at an ice front. Post-glacial erosion of the landscape by rivers has also produced characteristic landforms, including river gorges that have cut into superficial deposits and bedrock. Together, the sedimentary landforms and erosional features tell a dramatic story of landscape change during and since the last glaciation.

Figure 9 – Superficial deposits map of the CAVLP area. Locations of sites and selected place names are also shown. Grid is British National Grid with 10 km between tick marks. 3.2.1 The dynamics of a glacier margin – Bonnington and the Falls of Clyde During the last glaciation a vast ice stream flowed across the region from the west as major glaciers, sourced from the West Highlands and Southern Uplands, coalesced in the Lanarkshire area and streamed eastwards into the Firth of Forth. As climate warming gathered pace around 17,000 years ago, the melting ice stream retreated west and rivers fed by meltwater carried large quantities of sand and gravel east via the catchment of the River Esk in Midlothian. As the ice reached the Carstairs – Lanark area, the Highland and Southern Upland glaciers began to 14


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‘unzip’. This complex separation of the ice masses, together with the flat terrain, resulted in the ponding up of meltwater in ice-marginal lakes and the deposition of large tracts of ice-marginal sand and gravels (Figure 10).

N

Figure 10 – Google Earth image of a section of the Greenland ice cap. The image has been rotated to approximate the scenario envisaged for the western half of the Midland Valley during deglaciation. The ‘unzipping’ glaciers are depositing sand and gravel at their margins and in proglacial lakes. A region of moundy sand and gravel that was deposited in front of an ice margin occurs at Bonnington (2895, 6430), just east of Lanark (Figure 11). The area contains a high ridge of sand and gravel thought to mark the position of a former ice front and a number of deep depressions, called kettle holes, formed by the melting of ice buried under sediment at the glacier margin (Figure 11). The undulating terrain of ice-contact deposits gives way eastwards into flatter ground associated with an outwash plain deposited in front of the glacier. The sand and gravel from this outwash plain is currently extracted from a quarry at Hyndford (2902, 6417), just to the east of Bonnington. An elongate ridge of sand and gravel up to 25 m high and over 1 km long, called an esker, can be seen at Linnhead (2882, 6404), just to the south of Bonnington Linn (Figure 11). The esker formed when gravel carried by meltwater streams flowing in tunnels beneath or within the ice was deposited close to the ice margin and left behind as the glacier melted. The feature is a smaller version of the large sinuous esker ridge at Carstairs, approximately 8 km to the northeast. The Carstairs esker was formed during an earlier stage of ice retreat across the central lowlands and has been protected as a SSSI. The sand and gravel deposits of the Bonnington area overlie a valley that was infilled with sediment when it was over-ridden by ice during the last glaciation (Figure 11). Known as a ‘buried valley’, it was discovered during drilling and excavations for the Bonnington Power station. Thought to be the former valley of the River Clyde, it lies approximately half a kilometre to the north of the current river which follows the Falls of Clyde.

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Figure 11 – Map of the glacial deposits and landforms of the New Lanark and Bonnington area. The River Clyde flows northwards through the area. Aerial photography © UKP/Getmapping Licence No. UKP2006/01 The complex of ice-marginal sand and gravel deposits around Bonnington and Linnhead flank the deep rock gorge of the Falls of Clyde, a geological and biological SSSI, nature reserve, and part of the World Heritage Site of New Lanark and the Falls of Clyde (Figure 11). The gorge forms a vertically-walled slot up to approximately 50 m deep, cut into the Devonian sandstone. Through the 2 km long gorge, the river falls more than 60 m in elevation, dropping over the three waterfalls: Dundaff Linn, Corra Linn and Bonnington Linn. Located in the deepest part of the gorge, the spectacular Corra Linn is a two-step fall approximately 27 m high that opens into a large ‘amphitheatre’ at its base (Figure 12). Bonnington Linn, the uppermost waterfall, is a horseshoe-shaped fall formed from two vertical falls intersecting at right angles. The falls, and the angular bends of the gorge, are controlled by joint planes in the Devonian sandstones. The stepped nature of the falls arises from the gentle downstream dip on the rocks and the presence of thin, less resistant siltstone or mudstone beds within the sandstone sequence. These softer rocks are more easily eroded, undermining overlying sandstone units which are then broken off and carried away by the flow. The gorge of the Falls of Clyde contains little sediment, and rock is well-exposed in the stream bed. Near Dundaff Linn, small circular potholes have formed in the stream bed by the scouring action of cobbles carried in flow eddies. Despite the presence of these small potholes, there is little evidence for abrasion of the bed by sediment. The angular nature of the channel bed, clearly 16


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controlled by bedding planes and joints within the rock, indicates that erosion of the stream bed took place largely by the dislodging and removal of blocks of bedrock, a process called plucking. The size of blocks moved is consistent with flows of extremely high stream power arising from high discharges within the steep, confined channel. The form of the Falls of Clyde gorge, and its association with the ice-marginal sand and gravel deposits at Bonnington and the buried former valley of the Clyde, indicate that the formation of the gorge is most-likely related to drainage of an ice-marginal lake. With the preglacial Clyde Valley blocked by sediment, and the presence of the glacier blocking drainage to the west, meltwater ponded up in front of the ice forming a lake covering the flat ground southeast of Lanark. As the ice melted, the ponded water breached the ice dam to the west, forcing under the thinning ice and excavating the deep gorge along the Falls of Clyde. Near Bonnington Power Station, the outflow stream re-joined the original course of the Clyde Valley. Below this point, down to the area of New Lanark, the gorge broadens to a steep-sided valley that is partially infilled with sand and gravel deposits. Along the western side of the valley near Greenhead Gate (2877, 6420), a curving meltwater channel developed in sand and gravel deposits is perched 60 m above the River Clyde (Figure 11). The meltwater channel was once landscaped and the construction of a small dam at its northern end formed a small lake that is now infilling with vegetation. The partial fill of glacial sand and gravel in the Clyde Valley in this area indicates that the fill of glacial sediment was excavated by the meltwater stream during the drainage of the ice-marginal lake.

A

B Figure 12 – Photographs of the Falls of Clyde. (A) Historic image of the gorge below Bonnington Linn taken in 1913, view looking north (BGSŠNERC. All Rights Reserved. 2015; archive number P002344). (B) The lower section of Corra Linn, view looking south. 17


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3.2.2 Glaciers to rivers - the postglacial reshaping of the land The alteration of river courses through the cutting of new valleys, as seen at the Falls of Clyde, forms a characteristic feature of the region. Infilled valleys and deep gorges, along with evidence for the formation of pro-glacial lakes, are found throughout the CAVLP area, reflecting extensive reconfiguring of the drainage system during and after glaciation. The network of young valleys formed during this period include the deeply eroded channels of the Mouse Water, River Nethan and River Avon, as well as the many smaller streams including Fiddler Burn, Jock’s Burn and Garrion Gill (Figure 13).

Figure 13 – The system of buried pre-glacial valleys and rock gorges along the Clyde Valley between Hamilton and Garrion Burn (BGS©NERC. All Rights Reserved. 2015: Map reproduced from Paterson, McAdam, and MacPherson, 1998, p.55) The ‘Nemphlar channel’ at Auchenglen (2854, 6461) is a 3 km long dry valley truncated at its southern end by the gorge of the Mouse Water and its northern end by the deeply incised Fiddler Burn (Figure 14). The channel is mantled with glacial till, a deposit of compacted clay and stones formed under ice, which is overlain in places by ice-marginal sand and gravel deposits. These glacial deposits indicate that the Nemphlar channel is an old river valley that was buried beneath the glacier during the last ice age but was only partially infilled. The elevation of the channel is similar to the level of the Mouse Water above the gorge of Cartland Craigs (2871, 6447). This coincidence, combined with the location of the channel suggests that it may have once carried the Mouse Water north-west from Cartland Bridge (28686, 64436) to join the Clyde 18


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along what is now the lower reach of the Fiddler Burn (Figure 14). The Nemphlar channel was likely abandoned when erosion along the Mouse Water cut a gorge that breached the narrow ridge separating the channel from the main Clyde Valley. It is possible that this erosion may have arisen in a similar manner to that of the Falls of Clyde, with ice blocking the Mouse Valley at Cartland Bridge and damming a short-lived lake upstream. The new course into the Clyde may have been initiated by the cutting of an outflow channel as the ice dam was breached during melting and retreat of the glacier front. Following ice retreat the Mouse Water continued to flow in the new gorge to the Clyde, bypassing the Nemphlar Channel.

Figure 14 – Map showing the possible former course of the Mouse Water along Auchenglen (‘Nemphlar Channel’). Elevation data © UKP/Getmapping Licence No. UKP2006/01

Figure 15 – Sampson’s Slingstane, near the Fiddler Burn, south of Braidwood. The sandstone boulder is approximately 4 m high, view looking east. 19


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The enigmatic boulder of Sampson’s Slingstane (2846, 6470), which is perched on the rim of the gorge of the Fiddler Burn, is located close to its junction with the western end of the Nemphlar Channel (Figure 14). The stone is a 4 m diameter block of coarse-grained sandstone of unknown age and origin (Figure 15). The stone may have been part of a moraine formed along a former ice margin associated with a glacier blocking the western end of the Nemphlar Channel. Removal of other morainic debris during floods along the gorge, perhaps associated with drainage of an ice-dammed lake along the Fiddler Burn, may have left only the massive boulder behind. Alternatively, the stone may have been eroded from the gorge walls, and carried to its position in catastrophic floods occurring during or soon after deglaciation. The Lower Nethan Gorge, through which the River Nethan enters the Clyde Valley at Crossford, has been cut postglacially to the south of its original course. The pre-glacial River Nethan formerly joined the Clyde Valley via an infilled channel c. 1.5 km to the north near Overton. Similarly, the Avon Gorge at Ferniegair represents a newly cut valley carrying the Avon to the north of its former course along a now buried valley joining the Clyde Valley at Allanton (Figure 13).

A

B

C

D

5 km

Figure 16 – Sand and gravel deposits at Chatelherault. (A) Historic photograph from Chatelherault sand and gravel pit c. 1902 (BGS Archive: P239944). (B) Historic photograph of the Ferniegair sand pit c. 1921 (BGSŠNERC. All Rights Reserved. 2015; archive number P000075). (C) Panoramic image of the hunting lodge at Chatelherault with the former backscarp of the sand and gravel pit in the centre of the image. The removal of up to 10 m of sand has formed the low area of parkland to the right. (D) Generalised sketch of the relationship between the glacier, pro-glacial lake and delta system at Chatelherault.

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The landscape of the Ferniegair area is underlain by a thick deposit of sand that was formerly extracted from a large pit directly in front of the hunting lodge at Chatelherault (Figure 16). The sand forms part of a system of deltas that were deposited by the River Avon and other streams draining into a pro-glacial lake, “Lake Clydesdale”. The lake formed in the middle section of the Clyde Valley, upstream from an ice dam in the vicinity of Blantyre, approximately 6 km northwest of Chatelherault (Figure 16). It was probably the last major lake to form in the Clyde Valley during deglaciation. Drainage of this lake, which carried vast quantities of sand into the Glasgow area that have since been covered by glaciomarine and marine deposits, may have accompanied and/or driven final disintegration of the glacier occupying the Firth of Clyde. Within the Clyde and Avon Valley area, the modern River Clyde exhibits a wide range of channel types, including high energy, bedrock floored streams and gently flowing meandering alluvial channels. A good example of an alluvial channel meander can be seen along the Clyde Walkway between Mauldslie Bridge and Garrion Burn (Figure 17). In this area, the river flows between steep banks of silt, and during floods fine sediment is deposited along the valley floor forming the broad floodplain on the inner bend of the meander which provides valuable agricultural land. The high-energy character of the River Clyde can be seen in the rocky waterfall and gorge section at Stonebyres Falls. The rocky streambed at the falls displays a range of features including potholes and plucked blocks that are indicative of the main erosion processes by which rivers cut channels into resistant rocks.

A

B Figure 17 – Modern river environments of the Clyde Valley. (A) View of the meandering alluvial channel near Garrion Tower. View looking east. (B) Upper section of Stonebyres Falls, view looking east. A small cylindrical pothole, partially filled with water, can be seen in the left foreground. 21


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PEOPLE, ROCKS AND LANDSCAPE

The geology of the CAVLP area is strongly linked to many aspects of the regions heritage. Geological resources have long been exploited through mining, quarrying and power generation, activities which continue to this day. The region’s scenic character and environmental diversity, which have attracted tourists and inspired artists for centuries, are also dependent on its rocks and landscape. The diversity of the local heritage provides many opportunities for linking the geology to the region’s archaeology, industrial and cultural history, and biodiversity. Some observations on these links arising from the geological assessment are introduced below. These may be further developed through consultation with local heritage groups, and others with knowledge of the regions ecology and archaeology. 3.3.1 Geology and industry Evidence for former coal, sandstone, and sand and gravel workings can be seen in many places in the area, particularly at Chatelherault where all were formerly extracted. The industrial heritage of this area can be explored through the ‘Hole Story’ walking trail, which follows the route of the old mineral railway along the Avon Gorge, and the excellent displays at the Chatelherault Visitor Centre. The most spectacular example of former sandstone extraction in the area are the caverns from underground stoop and room workings at Threepwood Quarry (Sandyholm Caves). The quarry area and entrance to the caverns can be accessed through woodland although there is no path or public right of way to the site. Within the caverns, several old beams and wooden wedges are still in place as supports for the massive sandstone bed that forms the quarry roof (Figure 7). A thorough site assessment of any potential hazards of the underground workings should be completed if the site is to be included in the geological trail. Dramatic evidence of former workings, including open adits, can also be seen in the crags along the Lower Nethan Gorge, although the site is difficult to access. The former roadstone quarry at Stonebyres (near Blackhill) can be accessed, but the quarry faces are high and may be unstable in places (Figure 5). It is not known who owns the site. Although the extraction of coal and stone has largely ceased in the area, the sand and gravel deposits in the region east of Lanark continue to provide an important economic resource. The waters of the Clyde and Avon have long provided the power to support local industry and communities. The important role of water power for local industry can be seen most clearly at New Lanark, where the Clyde was diverted by weirs to drive the machinery for textile manufacturing as it drops steeply through the Falls of Clyde. The mills of New Lanark, set up in 1785, became the site for Robert Owen’s ‘Great Experiment’ in social reformation and are now protected as a World Heritage Site. The hydroelectric power stations constructed at Bonnington and Stonebyres in the mid 1920’s were the first large-scale renewable electricity scheme to be developed in the UK. These schemes use the natural flow and fall of the river to power turbines and produce enough power for 17,000 homes. 3.3.2 Geology, landscape and the environment The deep gorges that occur throughout the CAVLP area are unsuitable for agriculture or other development and many harbour ancient woodlands with great biodiversity. The woodlands of Cartland Craigs and Cleghorn Glen, the Lower Nethan Gorge, the Falls of Clyde, and the Avon Gorge at Chatelherault form the Clyde Valley Woodlands National Nature Reserve. The Falls of Clyde Reserve, managed by the Scottish Wildlife Trust, provides a great deal of information on the local wildlife in its visitor centre at New Lanark. 22


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The landscape of the Clyde Valley has long been visited by writers, artists and poets and was a source of inspiration for many during the Scottish Enlightenment. The dramatic settings along the Falls of Clyde in particular have been famously painted by Jacob More and J M W Turner, and inspired William Wordsworth and Sir Walter Scott amongst many others. The area has also been strongly influenced by the eighteenth century development of designed landscapes. Many of the former estates of the Clyde Valley, including Bonnington, Corehouse and Dalziel, developed walkways, gardens, bridges, and woodland to enhance the natural features of the landscape. The geography of the area has also strongly influenced the distribution of archaeological sites. Many historic sites are associated with strategic locations in the landscape, exploiting the defensive positions of high ground associated with resistant igneous rocks, such as the Iron Age hillfort at Blackhill, or utilising the protection of the deep gorges cut by glacial meltwater. The many castles built adjacent to gorges include Craignethan Castle (Lower Nethan Gorge), Cora Castle (Falls of Clyde) and Castle Qua (Cartland Crags). The inaccessibility of the deep gorges has also given rise to particular importance of river crossing points. Prior to the last century, these were restricted to fords or ferry crossings exploiting the shallow, quieter channel reaches above Bonnington weir at Tulliford, and at Clydesholm, west of Lanark. The spectacular Cartland Bridge, designed by Thomas Telford, crosses the Mouse Water at the lower end of the gorge of Cartland Craigs. The depth of the gorge at this point makes Cartland Bridge one of the highest in Scotland.

4 Shaping the trail The landscape reflects the interactions between the rocks, the erosional and depositional processes that shape the land, and people. The narrative of these interactions can be articulated through key sites, both through their own histories and their setting in the wider context of the Clyde and Avon Valleys. One approach to developing the geological trail is to focus on the histories of the key sites. The geological story of these sites may be told through geological resources designed to help people uncover the history in the rocks and landscape. This ‘site focus’ approach would develop a network of semi-independent sites telling the parts of the geological story relevant to each location. A more integrated approach would be to present the geological narrative as a whole, perhaps through the use of a booklet, website or app, which links the sites and demonstrates how they relate to the regional story. In this case, the trail would have a ‘story focus’, with the potential to incorporate a wider number of sites by including those for which the on-the-ground features may be harder to highlight on-site due to their scale or other restrictions (e.g. the river gorges). 4.1

SITE FOCUS

The potential for inclusion of individual sites in the geological trail is summarised in Table 1; a ‘traffic light’ system is used to rate different elements of the sites. The geological significance or ‘value’ of the site is considered in terms of their contribution to the two main elements of the wider geological story: 1) the history of the ancient Devonian and Carboniferous rivers that can be read in the rocks, and 2) the dynamic history of the glacial and postglacial streams that have reconfigured the landscape in more recent geological times. In terms of the geological significance and heritage and ecological associations, green indicates high value, amber moderate value, and red little or no value. With regard to the nature of access, red indicates the geological features may be difficult or dangerous to access, amber indicates features that may be

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accessed by rough paths, and green indicates that many features can be accessed directly from well-maintained paths. In the following discussion, sites have been classed as ‘key locations’ where they have high geological significance and good access, ‘potential locations’ where they have high geological significance but poor access and ‘regional locations’ where the geological significance is best considered in terms of the regional story. Geological Significance Rocks & ancient rivers

Site

Postglacial rivers

Heritage & ecological associations

Nature of access

Falls of Clyde Chatelherault Visitor Centre Key sites

Avon Gorge Blackhill

(Viewpoint)

Stonebyres Quarry Stonebyres Falls Clyde Meanders Baron’s Haugh

Potential sites

Lower Nethan Gorge

(With respect to regional story)

Threepwood Quarry (Sandyholm caves) Fiddler Burn

(With respect to regional story)

Regional sites

Sampson’s Slingstane Morgan Glen

(With respect to regional story)

Millhaugh

(With respect to regional story)

Cartland Craigs and Cleghorn Glen

(With respect to regional story)

Table 1 – ‘Traffic Light’ summary of geological sites in the Clyde and Avon Valleys. Key locations fall in the top section, potential locations in the middle and regional locations at the base. 4.1.1 Key locations – good geology and good access Falls of Clyde and Bonnington The Falls of Clyde provide the best exposed and most accessible examples of Devonian sandstone rocks in the area. Exposures occur throughout the gorge and particularly adjacent to the main footpath near Bonnington Linn. Together, the Falls of Clyde and the Bonnington area to the east provide the most dramatic evidence for how the dynamic action of water at a glacier margin can shape the landscape. The existing Scottish Wildlife Trust leaflet linked to the main Falls of Clyde trail along the gorge, provides good geological information relating to the Devonian sandstone rocks and the 24


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formation of the gorge and waterfalls. The geological story at the site could be developed further by extending the trail into the Bonnington area to integrate the story of the gorge with the adjacent ice-marginal sand and gravel system and evidence for the proglacial lake. An extended trail leaflet could be developed along with information panels at key locations to help people discover the story on-route. Alternatively an online approach could be used to provide ‘virtual information panels’. The advantage of the latter approach is that interactive resources could be developed to help users examine outcrops by the trail and identify landforms to help them discover the geological history for themselves. Additionally, multimedia including animated film and/or narrated aerial footage filmed from an unmanned aerial vehicle (UAV) could be used to show how the landscape of the area developed. Chatelherault and the Avon Gorge The Chatelherault Visitor Centre also has excellent resources for explaining the geological history of the area, including a geological trail leaflet, ‘The Hole Story’, which is available for users of the walking trails along the Avon Gorge. The gorge provides the best access in the area to Carboniferous rocks of the Scottish Coal Measures Group. Sandstones from the Scottish Upper Coal Measures and Scottish Middle Coal Measures are visible in quarries and sections along the trails (particularly the Mineral Railway Trail). Views of thicker sequences of strata can be seen in the crags on the opposite side of the river near Hoolet Row. These sections demonstrate the cyclic nature of the Carboniferous rocks and may add an additional geological element to the existing information provided. It would be possible to use a leaflet, information panel, or app to explain the layers of rock seen in the crag. The Chatelherault area, including the Avon Gorge, demonstrates the relationship between the new rock gorges cut by postglacial rivers and the old ‘buried’ river courses. In addition, the sandy glaciolacustrine delta deposits that built up at Ferniegair where the River Avon entered ‘Lake Clydesdale’ are a significant component of the postglacial history and have been an important economic resource. The scale of the postglacial rivers story, as demonstrated by the proglacial lakes, gorges and buried valleys, makes it difficult to narrate directly from sites on the ground. Multimedia resources including interactive maps or animations could be used to show how the landscape of the area developed. The Chatelherault Visitor Centre already contains a wealth of information about the geological history of the area. To build on this resource, an app or interactive website could be used to connect the geological story with people’s experience of the landscape. Blackhill The summit of Blackhill provides panoramic views over the Lanark area and central Clyde Valley. The site could be used to tell the regional geological story through an onsite information panel, leaflet or app. Methods that could be used to tell the story include animated film, interactive app, or cartoon-strip. The site also has additional value in relation to the igneous rocks underlying the hill, and strong heritage links as a strategic and defensive site. Nearby Stonebyres Quarry is an excellent site to observe the nature and structure of the resistant igneous rocks that form Blackhill, but access to quarry faces would require a thorough site assessment and ownership of the quarry is not known. Clyde Walkway The Clyde Walkway offers a number of opportunities to highlight present-day examples of river processes associated with the River Clyde, and develop links between the river environments and aspects of the geological history. River meanders can be seen along the walkway between Mauldslie Bridge and Garrion Tower and features associated with erosional channels occur at Stonebyres Falls. In the latter case, views of the falls are restricted by the steep gorge and trees, and whilst access to the falls down 25


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the gorge is possible off the walkway it is not advisable for the public. Some removal or pruning of trees may improve the view of the falls. The ponds at Baron’s Haugh provide a good example of how subsidence following shallow underground mining has shaped the river landscape. A series of walking guides are available for the Clyde Walkway, describing the geography and local features passed along the trail. A related geological guide for the Clyde and Avon Walkways could be produced to highlight the geological features passed on route. This could be in the form of a leaflet or small booklet, or could be a ‘virtual guidebook’, presented as an app or website. In relation to the wider story of the area, the modern river environments seen along the Clyde could be compared with those of the ancient Devonian and Carboniferous rivers that we know from the rocks, and the landforms carved by the glacial rivers, to explore the changing nature of rivers through time. 4.1.2 Potential locations - good geology but poor access Threepwood Quarry (Sandyholm Caves) The ‘caves’ extending underground from Threepwood Quarry near Sandyholm provide very good exposures of Carboniferous sandstone. The site is also very interesting for the heritage associated with the quarrying and probable use of the stone in the construction of Hamilton Palace. However safety issues with regard to access to the underground caverns must be considered carefully before decisions are made whether to include the site in the Trail. A ‘virtual site’ approach could be considered, using film and/or other multimedia. Lower Nethan Gorge The best examples of Carboniferous rocks seen in the area are along the crags within the Lower Nethan Gorge. The cyclic nature of the strata, sedimentary structures in channel sandstones, presence of coal and ironstone, well-preserved plant fossils, and evidence of former coal workings can all be observed within the Limestone Coal Formation. However, access to the crags is difficult in general and dangerous in places. Construction of safe access trails could enhance the site. A less invasive option would be to create a ‘virtual site’ by, for example, creating a film of a geologist exploring the site (“GeoCam”?). Fiddler Burn and Sampson’s Slingstane The gorge of the Fiddler Burn and the large boulder of Sampson’s Slingstane, located on the gorge rim, together form an intriguing geological site. There are good sandstone features exposed in the gorge and mudstone boulders and coal fragments in the stream bed demonstrate the supply of tipped waste from upstream. The enigmatic boulder perched on the edge of the gorge provides an interesting, if poorly understood feature. Access to the site requires crossing of fences and the gorge is steep and densely vegetated; public access is therefore not advisable. A virtual site approach similar to the Lower Nethan Gorge could be taken for this site. 4.1.3 Regional locations River gorges The woodland nature reserves of Cartland Craigs, Cleghorn Glen and the Lower Nethan Gorge are all formed in the deep valleys cut by postglacial streams. Together with the Falls of Clyde, the Nemphlar Channel and the Avon Gorge, these features demonstrate the dramatic postglacial reconfiguring of the drainage system of the Clyde catchment. In addition, every gorge has its castle; castles located on the rims of the gorges include Craignethan Castle on the Lower Nethan Gorge, Castle Qua at Cartland Craigs, Cora Castle at the Falls of Clyde, Cadzow Castle on the Avon Gorge and Cot Castle on the Avon near Stonehouse. Despite the significant relationship between these features and the geology, and the strong ecological and heritage links, the physical scale of the gorges and the restricted views due to the 26


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woodlands means that it is difficult to tell their geological story from individual sites on the ground. The significance of the gorges may be best developed through the use of a ‘story focused’ approach (discussed further in the next section) which would allow the features and their significance to be presented through the regional narrative. This approach would also be a good way to highlight the network of former defensive and strategic sites associated with the gorges. Millhaugh and Morgan Glen The Avon Walkway near Millhaugh and the River Avon in Morgan Glen provide fairly accessible examples of strata belonging to the Scottish Lower Coal Measures and Scottish Middle Coal Measures. Along the Avon Walkway, relatively rare exposures of mudstone and siltstone can be seen where the walkway crosses an eroded gully that joins the Avon 300 m north of the Millhaugh Bridge. The geological interest of these rocks is limited however as minor coal horizons within the rocks are not visible from the Avon Walkway. Along the Avon in Morgan Glen, sandstone is exposed in a small waterfall and cliffs along the opposite bank of the stream. The geological interest in the sandstones is limited and exposures are extensively covered by moss. There are also better examples of waterfalls and gorge morphology elsewhere in the CAVLP area. These sites could warrant short inclusions in the general regional narrative, or as locations within a “Clyde and Avon Walkway geological trail”, but do not offer significant interest as geological sites to support the development of detailed site-specific resources. 4.2

STORY FOCUS

Collectively, the geological sites and features of the Clyde and Avon Valleys tell a dramatic story of the development of the rocks and landscape over 400 million years; they also demonstrate the strong and diverse links between the geological past and the lives and livelihoods of the regions communities. Although elements of this story can be highlighted through the features seen at the key locations highlighted above, the dynamic nature of the geological processes that have shaped the landscape and the area’s significance to the wider geological history of Central Scotland can only be revealed by demonstrating how the features of different sites and locations are related to each other. Placing sites within the context of this wider narrative would maximise their value as components of the rich and diverse story of the shaping of the land. From a geological perspective, the rivers stand out as the strongest narrative thread. Rivers are a common link between the ancient Devonian and Carboniferous river systems forming the rocks, the dramatic postglacial development of the network of young valleys, and the modern gills, burns, and rivers of the Clyde and Avon valleys which remain a source of power, havens for woodland and wildlife, and places of recreation and creative inspiration. Centring the geological trail around a core narrative that could be told in a booklet or using a multimedia approach (website/animated film/app) would provide opportunities to: 1) develop coherent links between key sites, 2) give context that demonstrates the importance of the CAVLP area to understanding the geological history of central Scotland, and 3) provide a platform for inclusion of sites, such as the network of river gorges, that are not so amenable to presentation at specific sites due to their large scale. The narrative approach also has potential to help encourage people to explore the landscapes history for themselves by showing how observations made at sites on the ground can tell us about the ‘hidden’ history of the wider landscape.

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5 Conclusions and recommendations There are many good quality geological sites within the Clyde and Avon valleys through which the dynamic nature of the landscape’s history is revealed. In combination with the diverse local heritage which includes mining and quarrying, historic buildings and strong associations with Scotland’s cultural history, the geological sites can be used to demonstrate a dramatic geological history extending back 400 million years and in which, in recent times, local people have played an intimate part. The key sites of the Falls of Clyde and Chatelherault are already sites of geological interest, with considerable information provided through walking trail leaflets and displays at the Chatelherault Visitor Centre. Developments that could enhance the geological story told through these sites, and other localities in the area, include: 

  

Extending the Falls of Clyde geological trail leaflet developed by the Scottish Wildlife Trust to include the Bonnington area, linking the gorge with the depositional landforms that tell us about the ice margin and the formation of the glacial lake associated with the gorge’s formation. Developing a geological guide for the Clyde and Avon walkways to highlight the key geological features seen along the routes. Production of a leaflet explaining the formation of the rock gorges of the Clyde Valley to accompany the Clyde Woodlands National Nature Reserve walking trails leaflet. Developing information panels or online resources for Blackhill, utilising the viewpoint to tell the regional story of the landscape.

There is considerable potential for the use of novel and creative online and multimedia approaches to tell the dramatic history of the landscape and demonstrate its significance in the wider geological story of Central Scotland. Some suggestions include:  

 

Production of a film that integrates aerial footage, observations from sites and animations to tell the story of the shaping of the landscape. This could be shown at visitor centres in New Lanark and Chatelherault and featured on a website. Development of a website for exploring the geology of the area through interactive maps, images, animations and films. This could provide links to virtual information panels for key sites and to films or images for ‘virtual sites’. o Virtual sites could present the geological features of hard-to-access locations, making valuable geological sites accessible where actual site visits are not advisable due to safety issues or other access restrictions. o An app version with maps providing links to the ‘virtual information panels’ could be developed for users to take into the field. Web based educational tools, such as an interactive app, could be developed for some key sites to help users to explore how to, for example, observe sedimentary structures in the rocks and discover what they tell you about the landscape of the past. The interest of educational tools could be enhanced by using a ‘geocaching’ type approach in which sites could be marked by a system of codes marked on posts or small panels at key locations. Once the code is found, it could be entered into an app, providing access to the ‘virtual information panel’ for the location. Users could accumulate sites, recording geological features they have explored and put together the pieces of the geological story.

Some examples of geological trail resources that have been developed for sites across the UK are given in a list of website links in Appendix 2. The dramatic geological history of the CAVLP area and the strong and diverse links between the geology and the region’s heritage lend themselves to the development of innovative approaches to present the wider geological story of the shaping of the landscape. 28


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The scope of the Trail and the approach taken to present the story will be dependent the budget available and consideration of the potential users of the trail. The ideas presented above are intended to present possibilities for further discussion during the second phase of the geological trail project.

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Appendix 1 Site forms containing notes made at the sites during the field assessment. Photographs are provided on an accompanying DVD. Site Name

Falls of Clyde (east)

NGR

288120

642320

Location Falls of Clyde Nature Reserve; the eastern access to the reserve is located south of New Lanark and the reserve extends south along the eastern side of the gorge to Bonnington Linn. The Bonnington Power Station is located within the gorge. General Description The Falls of Clyde gorge comprises a 2 km rock gorge flanked by woodlands. The gorge contains a series of three waterfalls, Bonnington Linn, Corra Linn and Dundaff Linn. Geological Description The Falls of Clyde gorge is incised into coarse- to medium-grained, purple, micaceous sandstone of the Swanshaw Sandstone Formation, of Lower Devonian age. The sandstone is exposed locally adjacent to the main footpath, with the best exposure seen near Bonnington Linn. Here the sandstone is weakly cross-bedded and planar bedded. A 10 cm horizon at the base of the central sandstone bed contains red mudstone cobbles in a matric of very coarse sand indicative of a flood deposit. The sandstones are well exposed along much of the gorge, but access into the gorge is restricted. At low flow, the river bed is clearly visible, with bedrock exposed in many areas. Near Dundaff Linn, and above Bonnington Linn, the channel bed contains isolated small potholes and its form is strongly controlled by joint and bedding surfaces suggesting plucking has been the dominant erosion mechanism during gorge formation. The form of the waterfalls at Bonnington Linn and Corra Linn are also controlled by joint and bedding, with multi-step falls forming where less resistant 'shaly' sandstone horizons are preferentially eroded by the flow. The gorge has been interpreted as formed by erosion during meltwater outflow from a glacial lake developed upstream from an ice margin located in the Bonnington area. Location details of key features 288419, 641533

Dundaff Linn

288420, 641533

Corra Linn

288326, 640735

Bonnington Linn Viewpoint

288341, 640706

Bedrock exposure on footpath near Bonnington Linn

288398, 640735

Bonnington Power Station

Description of Access Access along the western side of the gorge is very good, with well-maintained trails and boardwalk between New Lanark to the Bonnington Linn. There are many viewpoints along the trail from which to view the gorge. There is a large parking area in New Lanark and visitor attractions including a cafĂŠ and the Reserve Visitor Centre are located in the village. The Visitor Centre contains informative displays about the local wildlife (but limited geological information). Trail waypoints are marked with symbols to highlight routes to heritage sites, gorge features and wildlife. Restricting conditions The steep gorge and impact of the hydropower scheme restrict access to the channel bed. Heritage Associations

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The historic mill village of New Lanark and the Falls of Clyde, from which the mills were powered, are together designated a World Heritage Site for their association with Robert Owen's 'Great Experiment' in social development in manufacturing. Bonnington power station constructed 1927 as part of the Lanark Hydro Electric Scheme, along with Stonebyres power station, the earliest hydroelectric scheme in the UK. Biodiversity Associations The woodlands of the Falls of Clyde Nature Reserve forms part of the Clyde Valley National Nature Reserve. There is a peregrine nesting site in the gorge and hide from which the nesting birds can be viewed. Currently available resources A geological trail leaflet produced by the Scottish Wildlife Trust is available for the trail between New Lanark and Bonnington Linn. The Falls of Clyde is described in the site review for the Geological Conservation Review series (McEwen and Werrity, 1993). Development opportunities Extend the current coverage of the geological trail (SWT leaflet) to include landforms in the Bonnington area and Linnhead Esker. Incorporate images and maps to show the buried channel of the Clyde, the association of the gorge and sand and gravel deposits and the former position of the ice margin at Bonnington.

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Site Name

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Falls of Clyde (west)

NGR

287780

641420

Location Falls of Clyde Nature Reserve; along the western side of the Falls of Clyde Gorge from Bonnington Linn and Linnhead Farm in the south, to Dundaff Linn and west to Greenhead Gate in the north. General Description The Falls of Clyde gorge comprises a 2 km rock gorge flanked by woodlands. The gorge contains a series of three waterfalls, Bonnington Linn, Corra Linn and Dundaff Linn. Geological Description The Falls of Clyde gorge is cut into sandstone of the Swanshaw Sandstone Formation of Lower Devonian age. A detailed description of the gorge is given in the site form relating to the eastern access of the gorge from New Lanark. Along the western side of the river, to the north of Corra Castle, the gorge is mantled with deposits of glaciofluvial sand and gravel. The deposits have an irregular, dissected morphology. Near Greenhead Gate there is an arcuate channel cut into the sand and gravel deposits that extends down the valley side to the north. The channel has been blocked by a small earth dam, creating a small pond that is now infilling with vegetation. To the south and west of Bonnington Linn, near Linnhead Farm, the Linnhead Esker occurs within the sand and gravel deposits. The esker is a long sinuous ridge typically 5 - 10 m high, but reaches approximately 20 m in height at its eastern end at Drummonds Hill. The ridge is described on historic geological maps as comprised of coarse to fine gravel. Location details of key features 288286, 640632

Bonnington Linn viewpoint 288206, 641418 Corra Castle 288366, 641459 Corra Linn viewpoint 287770, 642054

Greenhead meltwater channel

288100, 640395

Linnhead Esker

Description of Access Limited car parking can be found at West Lodge near Corehouse Farm. Access on the western side of the Falls of Clyde is very good, with numerous well maintained trails and tracks through the woods and along the gorge edge. Locally, some of the lesser used trails are overgrown but passable. The western and eastern trails along the falls of Clyde are connected by a footpath that crosses Bonnington Weir at the far eastern edge of the site. There is no crossing point over the Clyde to the west of this until the bridge at Clydeholm, west of Lanark. The Linnhead Esker is located in agricultural land and is not directly accessible by public right of way. Restricting conditions The steep gorge and impact of the hydropower scheme restrict access to the stream and lower parts of the gorge in many areas. Heritage Associations Corra Castle, perched on the rim of the gorge just upstream from Corra Linn, dates from the 14th 15th century. Local walks include a heritage trail covering historic sites on the east and west sides of the Falls of Clyde gorge. The landscaped pond near Greenhead Gate is not part of the heritage trail and condition of the tracks suggests it is not widely accessed. The specific history of the creation of the pond is not known but is considered likely to date from late 18th to early 19th centuries. During this period construction of designed landscapes to enhance the picturesque qualities of estates in the area was common practise. Biodiversity Associations

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The woodlands of the Falls of Clyde Nature Reserve forms part of the Clyde Valley National Nature Reserve. There is a Peregrine nesting site along the gorge and bat nesting in Corra Castle. Currently available resources The Falls of Clyde is described in the site review for the Geological Conservation Review series (McEwen and Werrity, 1993). Development opportunities See suggestions given in the Falls of Clyde east form.

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Site Name

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Chatelherault and the Avon Gorge

NGR

273674

653928

Location Chatelherault Country Park near Ferniegair, south-east of Hamilton. General Description The house of Chatelherault is the historic hunting lodge for Hamilton Palace (now demolished) located adjacent to the Avon Gorge near its confluence with the Clyde valley. The lodge is an established visitor attraction with an excellent visitor centre and cafe, and several trails following footpaths through the woodland along the gorge Geological Description The historic hunting lodge is constructed from yellow to orange sandstone that may have been sourced locally. Good sedimentological features associated with bedding and cross-bedding can be seen in the stone blockwork. A decorative fireplace in the lodge is made of Cambuslang marble. The lodge is underlain by sand and gravel deposited in a glaciofluvial delta. The parkland contains the scarp of the former edge of a quarry from which sand and gravel were excavated to within 40 m of the front of the lodge. Historic photos of the quarry are held in the BGS archives. The visitor centre contains extensive displays outlining the geological history, ecology and heritage of the area; including the formation of the Carboniferous sedimentary rocks, fossils, glaciation, postglacial development of the gorge, river habitats, local mining history (coal and sand and gravel) as well as the history of the house and surrounding park land. Through the Avon Gorge, the river runs through sedimentary rocks of the Middle and Upper coal measures formations. In the northern section of the gorge, purple to red micaceous sandstones of the Scottish Upper Coal Measures Formation are exposed along the Mineral railway path near Dukes Bridge. In places large-scale cross bedding and thinly bedded 'flaggy' horizons can be seen. The sandstones are shallowly dipping and form extensive flat surfaces along the bed of the stream which is fluted along the base-flow channel line. Approximately 250 m south from Dukes Bridge, the Scottish Upper Coal Measures Fmt is faulted down against the Scottish Middle Coal Measures Fmt, the fault is not seen, but there are exposures of Scottish Middle Coal Measures Fmt shaly mudstones along the track. The limestone forming the contact between middle and upper CM is marked on historic maps but not seen. Scottish Middle Coal Measures Fmt sandstones are exposed in crags along the gorge and along the river bank where accessible. Rarely coaly mudstone horizons are seen, mostly sandstone is observed. Shafts marked on old geological maps are poorly preserved. Down towards the white bridge (track closed due to landslip) a small shaft can be seen close to the river. Contaminated outflow, apparently from this shaft is seeping into the river. Along the river bank near the shaft a coal horizon occurs near the base of the river bank but it is poorly exposed due to vegetation and bank collapse and only accessible at low water - general access not advised. The best exposure of coal measures strata can be seen in the crag across the river from Hoolet Row ruins. Location details of key features 273547, 653805

Dukes Bridge

273582, 653613

Mineral Railway Path - sandstone exposure

273693, 652932

Hoolet Row - view of strata in crag across river

273482, 653964

Chatelherault - view of lodge and parkland

273672, 653932

Chatelherault Visitor Centre

Description of Access

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There is a large free car park, and easy access to the Visitor Centre (including disabled access). There is a network of well-maintained trails along the Avon Gorge with circular walks utilising bridge crossings. However, the White Bridge and associated path have been closed due to landslips arising from instability of the gorge. Rock exposures are accessible in places adjacent to the path and can be viewed in crags in places, and the river bank can be accessed in several places. Restricting conditions Tree growth may restrict views of sections in crags during the spring and summer. Access to river bank areas would be restricted during high flow conditions. Heritage Associations The hunting lodge of Chatelherault is a regionally important historic site due to its link with the now demolished Hamilton Palace. Across Dukes Bridge there is also the ruin of Cadzow Castle. The area has a history of quarrying and mining for sandstone, sand and gravel and coal. The mineral railway (now the 'Mineral Railway Trail') formerly carried coal from the Avon Valley to Hamilton. The visitor centre contains displays and information on the local mining heritage. Biodiversity Associations The woodland along the Avon Gorge forms part of the Chatelherault Country Park. Currently available resources There are excellent geological displays in the visitor centre covering most aspects of the regional geology and geoheritage. There are trail leaflets, including a geological trail 'The Hole Story' providing route information, and highlighting aspects of the geological and cultural heritage. Sign boards and information panels around the house and immediate grounds provide information on stone work and sand and gravel quarrying. Development opportunities An online resource such as an interactive app or webpage may complement existing on-site resources and leaflets. The site may benefit from resources that encourage geological exploration such as education tools to help users identify geological features and compare the features of modern rivers to what the rocks tell us about the rivers of the past.

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Site Name

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Blackhill

NGR

283355

643064

Location Hill top viewpoint near Stonebyres Holdings, west of Kirkfieldbank. General Description The top is a regional viewpoint over the upper Clyde Valley; to the east and north-east are Lanark and the narrow incised valley of the upper Clyde and the gorge of Cartland Craigs, to the north is the hidden dry valley of Auchenglen near Nemphlar, to the north-west is the lower ground towards Hamilton, to the south-west and south is the upper Nethan valley towards Lesmahagow. Geological Description The high ridge of Blackhill is underlain by medium to pale pinky-orange felsite, which can be seen in boulders in the grass near the hill's summit. As well as the felsite, there are boulders of porphyritic rock with red-brown matrix and abundant 1 - 5 mm cream coloured porphyroblasts (possibly altered feldspar). The porphyritic rock is similar to the dyke seen in the near-by Stonebyres Quarry. The intrusive igneous rocks can be seen well exposed in Stonebyres Quarry on the eastern flank of the hill. The view from the summit highlights the topographic fall of the landscape to the west as the hill sits close to the boundary between the Carboniferous strata to the west and the devonian strat to the east. The more resistant devonian sandstones are associated with the higher ground, and deeper, narrower sections of the Upper Clyde valley. To the west, the terrain is generally lower and the valleys broader. The site could be a key place to point out the up-valley movement of ice during the last glaciation and the distribution of glacial deposits and incised valleys. Location details of key features 283197, 643546

Blackhill trig point

Description of Access Access is off a single track road off the B7018 from Kirkfieldbank to Lesmahagow. Blackhill Viewpoint is signposted with brown heritage signage from the B7018. There is a small parking area with a style crossing over a fence into pasture. The hilltop is a short walk to the north-west along the edge of the field and crossing a second style. Restricting conditions The pasture used for grazing sheep and cattle. Heritage Associations Historic Iron Age fortifications on the hill summit are indicated by earth works, and there is also a Bronze Age burial cairn. Biodiversity Associations None known. Currently available resources None known. Development opportunities As the main viewpoint over the area, an on-site information panel or leaflet could be used to provide information about the geological history of the area. For a multimedia approach, an interactive app could be developed that overlays a geological interpretation of different stages in the history of the region on a panoramic image of the view from the summit

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Stonebyres Quarry

NGR

283588

643096

Location Former road stone quarry on the eastern flank of Blackhill, near Stonebyres Holdings. General Description The disused quarry is c. 150 in diameter, with quarry faces up to 15-20 m high. There are lower faces, c. 2-3 m high, in the middle area of the quarry. Concrete platforms and some parts of former quarry infrastructure remain. There are minor amounts of tipped waste including plastic waste and car tyres. The quarry floor is partially overgrown with medium-sized trees and shrubs Geological Description The bedrock comprises a pale orange to pinky-orange fine to medium-grained crystalline rock (felsite). Slightly inclined cooling fractures nearly the full height of the quarry are seen in the quarry faces, in places where the quarry faces are slightly overhanging, the polygonal nature of the fractures can be seen. The felsite is intruded by vertical dykes that have been left by the quarrymen as spines protruding from the quarry faces. The dyke rock is porphyritic with creamy-white crystals in a reddish-brown fine grained matrix. Location details of key features N/A Description of Access The site is accessed from the Blackhill parking area by walking c. 200 m east along the single track road. The entrance way has large boulders to prevent vehicle access but broken fencing leaves the quarry open to foot access. No signage relating to danger or restricted access to the site were seen during the site visit but the nature of the broken gate indicates access was formerly restricted. The faces of the quarry are clean and cooling joints are visible from the centre of the quarry. Smaller faces are accessible in the centre of the area. The high faces appear in good condition with relatively small areas of boulder deposits at the base. Restricting conditions Ownership of the quarry site remains unknown. Heritage Associations Historic geological maps indicate the quarry was formerly worked for road stone.

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Site Name

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Lower Nethan Gorge

NGR

28350

646990

Location Lower section along the River Nethan near Crossford, part of the Clyde Valley Woodlands National Nature Reserve. General Description 15 – 30 m deep gorge incised into bedrock by the River Nethan. The steep slopes of the gorge are wooded but rocky crags form prominent features on its north-west side. Geological Description The crags show excellent sedimentological features associated with the coal-bearing succession of the Limestone Coal Formation. The prominent crags are formed by two massive sandstone units, the uppermost exceeding 10 m thickness in places, and the lower most up to 4 m. The height of the crags increases from the middle of the gorge to the west suggesting increasing thickness of channel sand. The sandstone is buff to orange, medium- to coarse-grained and cross-bedded, with channel scours of very coarse sand to fine gravel. There are tool marks in places indicating some of the sandstone was formerly worked from the face of the crag. The base of the largest sandstone bluff can be followed for several hundred metres along the gorge. It contains many fossilised branches (lycopod) preserved as circular casts with rims of black organic matter. In paces the bark imprints are visible as casts. There are also dark mudstone 'slabs' caught up in the base of the sand unit possibly rip ups of peat or organic mud, some may be organic woody material. The sandstone passes from the tree branch layer into a massive coarse cross-bedded and channelized sand unit. Approximately 6 m up from the base of the sand is a knarled brown to white horizon c. 30-50 cm thick what look like roots and/or burrow traces indicative of a fossil soil. The base of the sandstone is a sharp contact with underlying finely laminated, dark grey, shaly mudstone with some siltstone laminae. Where the underlying sandstone unit is visible, the mudstone is c. 4 m thick. Approximately 50 cm below the base of the sandstone, coal horizons are present, and near the base of the mudstone there are large nodules of ironstone. In the middle of the accessible section of crags, a dramatic tunnel c. 3m diameter has been excavated upwards from the base of the sandstone. The tunnel is inclined and may have been some kind of access shaft for workings on the coal beneath the sandstone, or in strata lower down the gorge. Location details of key features 281873, 646640

Lower Nethan Crags

281593, 646476

Lower Nethan Gorge Viewpoint

281537, 646366

Craignethan Castle

Description of Access There is parking near the tourist information centre in Crossford. The gorge can be access via a trail from Crossford village, or from the car park at Craignethan Castle. The trail is a good path through woodland along the top of the gorge, with a viewpoint over the gorge near Craignethan Castle. Access into the gorge is difficult and dangerous due to the steep terrain. The crags can be reached by descending the steep slope near the centre of the gorge but public access is not advised. Restricting conditions The nature of the terrain restricts access to the best outcrops. Views of the gorge and crags from the viewpoint would be best in winter when vegetation has died back. Heritage Associations Craignethan Castle, built around 1530, is sited in a defensive position on the edge of the gorge. It is located in the core of a meander which forms steep cliffs on two sides of the site, with the deep valley of the Craignethan Burn to the north. There is evidence for former coal mining and minor quarrying of sandstone within the gorge.

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Biodiversity Associations The woodlands along the gorge are part of the Clyde Valley Woodlands National Nature Reserve. Currently available resources The Lower Nethan Gorge Nature Reserve is included in a trails leaflet for the Clyde Valley Woodlands. Development opportunities For safe public access to the site, construction of a safe access trail would be required. An alternative approach could utilise multimedia to create a virtual site, perhaps including film of a geologist exploring the crags.

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Site Name

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Stonebyres Falls

NGR

285297

644015

Location Stonebyres Falls (sometimes called Stonebyres Linn) are located on the River Clyde near Linnville, west of Kirkfieldbank. General Description Bedrock stream and c. 20 m high waterfall in Devonian sandstone, seen from the Clyde Walkway. Geological Description The waterfall and the channel bed upstream are cut into medium to coarse purple micaceous sandstone of the Swanshore Sandstone Formation of Lower Devonian age. The sandstone is crossbedded and contains irregular patches and horizons of pebbly sandstone. Stonebyres Falls comprise two rock steps; the upper is a step-fall approx. 3m high and the lower is a chute approximately 1518 m high. Both levels of the waterfall are associated with rock platforms which extend c. 10-20 m downstream from the initiation point of the fall in the centre of the channel. The falls and rock platforms are cut into massive, poorly jointed sandstone beds, with a thin eroded horizon between - possibly a more flaggy bedded or silty layer. The platform associated with the lower fall has a curved undercut at its downstream end indicating abrasion and/or cavitation associated with eddying or the breaching of a large pothole. The rock platform will be covered at highflow, whereas at low flow (as at the time of visit) the flow is constrained into a narrow central chute. Angular blocks derived by plucking from the sandstone are seen on the platform between the upper and lower falls. Location details of key features 285511, 644024

Stonebyres Weir

285297, 644015

Stonebyres Falls

Description of Access There is on-street parking on the A72 near Linnville or in Kirkfieldbank. Access to the site is via the Clyde walkway which crosses the Clyde across Stonebyres Weir. From the weir there are good views of the bedrock channel bed above the falls. Views of Stonebyres Falls from the Clyde Walkway are restricted due to trees and vegetation and the steep nature of the gorge. Access to the falls is difficult and dangerous; descent is down a steep vegetated slope above a lower cliff and not to be advised for the general public. Restricting conditions Views of the Falls may be better in winter when the trees are not in leaf. Heritage Associations The gorge below the falls was formerly the site of Cairnie Castle which has now been demolished. The Stonebyres power station was constructed in 1926-1927 along with the Bonnington power station. The hydroelectric power scheme was the first of its kind in the UK. Biodiversity Associations None known. Currently available resources The site is included as a feature of interest in the Clyde Walkway booklet (Crossford to Falls of Clyde, New Lanark). The falls are mentioned as a barrier to salmon and sea trout migration, no geological information is provided. Development opportunities Removal of some trees may enhance views of the falls. The site could be included in a geological guide to accompany the Clyde Walkway leaflets.

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Site Name

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Avon Walkway: Millhaugh to Fairholm

NGR

275218

650683

Location Section of the Avon Walkway from Millheugh Bridge to Fairholm, to the east of Larkhall. General Description The section of the Avon Walkway between Fairholm and Morgan Glen, west of Larkhall follows the west bank of the River Avon, and passes the village of Millheugh near Millheugh Bridge. Geological Description The River Avon does not follow a dramatic gorge in this section, but is cut into strata of the Scottish Lower and Scottish Middle Coal Measures. Sandstone is exposed in places along the banks of the Avon, but contains few interesting features. The overlying siltstone and mudstone succession is well exposed in an incised minor burn near Sunnyside. The section is visible from the footbridge and can be accessed fairly readily, although the ground is rough and there are several fallen trees across the burn. Minor coal seams are mapped in the succession on historic fieldslips, but as they are thin and do not form distinct features they were difficult to locate during the survey due to poor light. Minor evidence for surface workings and/or shafts associated with former coal workings can be seen near Fairholm, with others marked on historic maps Location details of key features 290223, 645408

Sunnyside Burn

Description of Access A small area for car parking is located off the roundabout near Millholm Bridge. The Avon Walkway can be accessed from the west side of the bridge. The Avon Walkway links to the north with the trails along the Avon Gorge at Chatelherault, and to the south with paths through Morgan Glen. Restricting conditions None known. Heritage Associations Some evidence for former mine workings in the area. Biodiversity Associations None known. Currently available resources None known. Development opportunities Limited on-site development opportunities. Possible inclusion of site in a Clyde and Avon Walkway geological guide.

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Morgan Glen

NGR

275250

650830

Location Morgan Glen is a small area of woodland and parkland located to the southeast of Larkhall. General Description Morgan Glen is a deep, steep-sided, wooded valley along the River Avon. Geological Description The deep valley at Morgan Glen has been cut by the River Avon into strata of the Scottish Middle and Scottish Lower Coal Measures formations. Sandstone outcrops are seen in places along the river bank, but the only good exposure found is at a small waterfall that is marked on the topographic maps of the area. Some 80 m upstream from the waterfall, layered strata of the Middle Coal Measures are well exposed in the west bank of the river at the base of a 15-20 m crag. The actual exposure does not appear to be accessible but can be seen from river beach on the eastern bank. Interpretation of the strata is hampered by overhanging vegetation and the weathered nature of the rocks. Location details of key features 275573, 650224

River Avon, Morgan Glen

275739, 650014

Small waterfall in Morgan Glen

Description of Access Morgan Glen can be accessed from the area of the Leisure Centre to the west of Larkhall, and from the east side of Millheugh Bridge. Main paths are tarmac in places, with numerous minor tracks through the woods. The river bank can be accessed but the rocks are very slippery and may be dangerous at higher water levels. Restricting conditions High water will restrict access to the river banks where rock sections are visible. Rocks on the riverbank are very slippery. Views of exposures are limited by overgrowth of vegetation. Heritage Associations Historic maps indicate an old limestone quarry within the glen, but the area is now heavily overgrown and no evidence for the quarry remains. Biodiversity Associations None known. Currently available resources A walking trail leaflet produced by South Lanarkshire Council is available for Morgan Glen but does not provide information on the geology or the River Avon. Development opportunities Development opportunities are limited as there are few good rock exposures at the site. It could be included as a minor location within a geological guide of the Clyde and Avon Valley Walkways.

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Clyde Walkway: Garrion Burn to Mauldslie Bridge

NGR

280360

650940

Location River Clyde walkway between Cardies Bridge (Garrion Burn) and Mauldslie Bridge. General Description The Clyde Walkway follows a meandering section of the River Clyde. Geological Description The Clyde valley here is underlain by strata of the Scottish Lower and Scottish Middle Coal Measures formations. The valley is much broader than in the section between Crossford and Lanark to the south, and the river follows a quieter, meandering course. In this section, the Clyde follows a wide meander, with a 3-4 m high terrace of alluvium forming a flood plain on the inside of the bend. The Garrion Burn joins the main stream via a small alluvial fan and small gravel bar has built up where the Garrion Burn meets the slow-flowing channel of the Clyde. Location details of key features 279061, 651167

Confluence of Garrion Burn with the River Clyde

280345, 650243

Mauldslie Bridge

Description of Access There is a small area for parking on Cardies Bridge over the Garrion Burn, and the Clyde Walkway can be accessed from the east side of the bridge. Signs indicate issues with 'antisocial behaviour' in Mauldslie woods. Restricting conditions None known. Heritage Associations None known. Biodiversity Associations Mauldslie Woods form part of the Clyde Valley Woodlands National Nature Reserve. Currently available resources The section of the walkway and trails through Mauldslie Woods are included in the trail leaflet for the Woodland Nature Reserve, and in the Clyde Walkway leaflet (Strathclyde Country Park to Cardies Bridge). No information about the river landscape is provided in these resources. Development opportunities Description of the river landscape and features could be included in a geological guide to the Clyde and Avon Valley Walkways.

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Site Name

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Sampson's Slingstane and Fiddler Burn

NGR

284570

647020

Location Section of the Fiddlers Burn near Fiddlers Leap, south of Braidwood. General Description Fiddler Burn flows through a rock gorge to the south of Braidwood, joining the River Clyde at Crossford. Sampson's Slingstane is a large boulder perched on the eastern rim of the gorge near Fiddlers Leap. Geological Description Fiddler's Burn is incised in to strata of the Limestone Coal Formation. A 6-10 m crag of sandstone forms the western bank of the stream directly below Sampson's Slingstane. At the base of the crag, a 20cm thick mudstone bed containing plant fossil imprints and some ironstone nodules is being preferentially eroded. The erosion of the mudstone has undercut the overlying sandstone by up to 2 m in places, exposing a bed of sandstone below with well-developed ripples on the surface of the bedding plane. The stream bed contains many boulders of soft mudstone with many plant fossils, these together with coal fragments in sandy bars suggests that much of the material is being sourced from mine waste upstream. Large slip faces in unconsolidated spoil tips (c. 15-20 m high) are found approximately 50 m upstream from the waterfall. Former quarries marked on historic maps to the east of the stream are overgrown with no exposures. Sampson's Slingstane is a massive, 4 m high boulder of coarse sandstone perched on the edge of a sandstone cliff within the gorge. The origin of the sandstone is unclear, and it is possible it has been locally derived. No records have been found pertaining to the origin of the boulder. The location of the stone, perched directly on the edge of the gorge within the deeply incised valley suggests that the emplacement of the stone may be related to the formation of the gorge. It may have been emplaced along with other morainic debris at a former ice margin blocking the western end of the Nemplar Channel. Drainage of a lake dammed by the ice along the Fiddler Burn may have cleared the surrounding debris, isolating the massive boulder which was too big to move. Alternatively, the stone may have been emplaced during a major flood within the gorge, most likely during or soon after deglaciation. Location details of key features 284571, 647023

Sampson's Slingstane

284572, 647056

Fiddlers Burn

Description of Access Access to the site is difficult. There is little parking on the Auchenglen Road and no footpath or public right of way to the site which lies down in the wooded glen beyond pasture fields. Fence crossings were required. Access through a birch wood brings you on to the remains of a quarry track with is vegetated and passable, but disappears at the edge of the beech woodland. Sampson's Slingstane is easily seen in the Glen from the old quarry track. Access to outcrops within the burn is down a moderately steep vegetated slope. Restricting conditions Access to along the bed of the Fiddler Burn is only possible in extremely low flow conditions. Heritage Associations Former quarries indicate historic sandstone extraction, and relatively large spoil tips upstream from the location of Sampson's Slingstane are indicative of former coal mining in the area. Biodiversity Associations None known. Currently available resources None known.

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Development opportunities The difficult of access to the site limits the potential for development opportunities. Construction of trails would be required to increase access. Alternatively, a 'virtual site' approach could be taken, utilising a multimedia to show the key features of the site.

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Site Name

Last modified: 2016/01/18 16:31

Baron's Haugh Nature Reserve

NGR

274900

654970

Location The lochs of Baron's Haugh are located adjacent to the River Clyde near Dalzell Park, to the south of Motherwell. General Description The site comprises a number of shallow lochs along the flood plain of the River Clyde that form an RSPB nature reserve. Geological Description The ponds of Baron's Haugh are found on the floodplain formed on the inside bend of a meander of the River Clyde. The main loch is not seen on historic topographic maps of the area (dating from 1864 - 1938), and is thought to have formed as a result of subsidence related to underground working of coal. The Dalzell and Broomside Colliery, Ross Colliery and Ferniegair colliery were all located within 1 km of the site. The loch is reportedly kept relatively warm in winter by the influx of water from underground workings. Location details of key features N/A Description of Access There is a carpark located off a minor road to the south of Motherwell that forms the starting point for a network of footpaths providing access to the site. Some of the paths are tarmac but most are cinder track. Several hides for bird watching have been constructed around the margin of the pond. The network of paths connects to the Clyde Walkway which follows the River Clyde to the south of the main loch. Restricting conditions None known. Heritage Associations The formation of the pond as a result of former mining forms a strong heritage link for the site, providing a fairly unique example of landscape change related to mining. The site is also linked to the former country estate of Dazell Park. Biodiversity Associations The loch and surrounding wetlands form an important habitat for a bird life, and are protected as an RSPB reserve. Currently available resources A leaflet for Baron's Haugh and Dalzell Estate has been produced by North Lanarkshire Council and the RSPB, providing a trail map and information about the heritage of the area. The site is also included in the leaflet for the Clyde Walkway (Strathclyde Country Park to Cardies Bridge). Development opportunities If the geological link to the loch can be verified, the history of the site could be included in a geological guide to the Clyde and Avon Walkways.

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Appendix 2 Links to selected online resources for Geoparks and geological trails across the UK Leaflets for walking trails (a few examples): SNH page on Scottish Geotrails with links to leaflets: http://www.snh.gov.uk/enjoying-the-outdoors/what-can-i-see/geology-rocks/geology-trails/ Fforest Fawr Geopark: http://www.fforestfawrgeopark.org.uk/geotrails/ Staffordshire GeoConservation: http://srigs.staffs-ecology.org.uk/Geotrails/Churnet/index.html Shropshire Geological Society: http://www.shropshiregeology.org.uk/Geotrails/Geotrails.asp 

Interactive online example: http://www.shropshiregeology.org.uk/Geotrails/TitterstoneClee/Titttrailagain.html#

Cumbria RIGs: http://www.cumbriarigs.co.uk/?Geological_Trails North York Moors: http://www.northyorkmoors.org.uk/visiting/see-and-do/forests-andwoodlands/forge_valley_geology_trail_tcm6-20853.pdf For Kids: http://www.dudley.gov.uk/EasysiteWeb/getresource.axd?AssetID=3582&type=..

Online information resources: Lochaber Geopark (for car-based trip with short walks) - Some information is provided on the website with more information and maps in leaflets that can be purchased online or in visitor centres: http://lochabergeopark.org.uk/explore-lochaber/lochaber-geotrails/ North Pennines AONB – Online video guide and leaflets e.g. Low Force and Holwick http://www.northpennines.org.uk/Pages/LowForceandHolwickgeotrailvideo.aspx http://www.northpennines.org.uk/Pages/PublicationItem.aspx?DocRef=94 Shetland Geopark “Shaping the landscape” webpages: http://www.shetlandamenity.org/shaping-the-landscape BGS resources of interest BGS GeoBritain (online map of UK geological sites and walks): http://www.bgs.ac.uk/discoveringGeology/geologyOfBritain/geoBritainMap/ BGS Geological Walk guide books: http://www.bgs.ac.uk/discoveringGeology/geologyOfBritain/GeologicalWalks/home.html BGS animated video on Carbon Capture and Storage: https://www.youtube.com/watch?v=4v2_4Dr2Gds BGS website – Blakeney Esker Explored (information on a key geological feature and what it reveals about the glacial history of parts of Norfolk): http://www.bgs.ac.uk/discoveringGeology/geologyOfBritain/blakeneyEskerExplored/home.html

Apps: Yorkshire Dales Millennium Trust – Geo Dales Project: http://www.ydmt.org/programme-details-geo-dales-project-15732 and Geo Trail The Settle App http://www.visitsettle.co.uk/app.html Abberley and Malvern Hills Geopark – Geopark Way App: http://geopark.org.uk/pub/2013/10/geopark-way-onyour-phone/ Fife Coastal GeoTrail App: http://www.apppicker.com/apps/1049261215/fife-coastal-geotrail-app Geopark Shetland App: http://www.shetlandamenity.org/geopark-app BGS Apps – iGeology - http://www.bgs.ac.uk/igeology/ and iGeology 3D - http://www.bgs.ac.uk/igeology/3d.html

Geology for fun: Control landscape evolution yourself: http://www.wired.com/2015/02/gorgeous-geology-app-explores-new-uxterritory/ Explore the structure of rocks: http://app.visiblegeology.com/profile.html

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Glossary Adit

A sub-horizontal tunnel or passageway leading into a mine

Abrasion

A process of river erosion whereby rock is worn down by the impact of grains of sediment carried in the flow.

Alluvial

Environments, actions and products of rivers or streams.

Bedding

A feature of sedimentary rocks, in which planar or near-planar surfaces known as bedding planes indicate successive depositional surfaces formed as the sediments were laid down.

Carboniferous

A geological period [359–299 Ma] of the Palaeozoic Era preceded by the Devonian and followed by the Permian.

Conglomerate

A coarse-grained clastic sedimentary rock, a significant proportion of which is composed of rounded or sub-rounded pebbles and boulders.

Cross-bedding

Sets of strata which are inclined to the general stratification of the beds. They dip in the direction of fluid flow at the time when the beds were laid down.

Devonian

A geological period [416–359 Ma] of the Palaeozoic Era preceded by the Silurian and followed by the Carboniferous.

Dyke

A sheet-like body of intrusive igneous rock emplaced along a vertical or near vertical fracture, normally discordant to the structure in the country rocks.

Esker

A sinuous ridge of sand and gravel formed by streams within or beneath glacial ice.

Felsite

A general term used to denote pale-coloured, fine-grained igneous rocks.

Fluvial

Referring to a river environment.

Formation

The fundamental unit used in lithostratigraphy. Specific features distinguish one formation from another. Formations may be subdivided into members and several formations may constitute a group.

Glaciofluvial

Refers to sediments deposited by flowing glacial meltwater.

Glaciolacustrine

Refers to deposits and landforms derived from materials brought by glacial meltwaters into lake environments.

Igneous rocks

A rock that has formed from the cooling of magma (molten rock).

Intrusion

A body of igneous rock which has been injected as magma into existing hard rocks (country-rock). On cooling the magma is called an igneous intrustion.

Joints

A fracture, or potential fracture, in a rock adjacent to which there has been no displacement.

Kettle holes

A hollow formed in glacial sand and gravel deposits by the melting of buried ice.

Limestone

Sedimentary rock composed mainly of calcium carbonate.

Meltwater

Water produced by melting of snow or ice.

Moraine

Accumulations of material which have been transported and deposited by ice.

Plucking

A process of river erosion involving the loosening, dislodgement and removal of blocks of bedrock from the channel bed.

Pothole

A roughly cylindrical erosional feature that forms in bedrock river beds by the grinding action of grains carried in eddying water.

Sedimentary rock

A rock formed in one of three main ways: by the deposition of the weathered remains of other rocks (clastic sedimentary rock); by the deposition of the results of biogenic activity; and by precipitation from solution. Four basic processes are involved in the formation of a clastic sedimentary rock: weathering (erosion), transportation, deposition and compaction.

Shaft

A vertical passageway excavated during mine working

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Bibliography British Geological Survey holds most of the references listed below, and copies may be obtained via the library service subject to copyright legislation (contact libuser@bgs.ac.uk for details). The library catalogue is available at: https://envirolib.apps.nerc.ac.uk/olibcgi. Published papers and reports BROWNE, M A E and MCMILLAN, A A. 1989. Quaternary geology of the Clyde Valley. British Geological Survey Research Report SA/89/1 FINLAYSON, A, MERRITT, J, BROWNE, M, MERRITT, J, MCMILLAN, A AND WHITBREAD, K. 2010. Ice sheet advance, dynamics, and decay configurations; evidence from west central Scotland. Quaternary Science Reviews. Vol. 29, 969–988. MCEWEN, L J and WERRITTY, A. 1993. Falls of Clyde. In Quaternary of Scotland. Geological Conservation Review Series, No. 6. GORDON, J E and SUTHERLAND, D G. (editors). (London: Chapman and Hall) MCLELLAN, A G, 1969. The last glaciation and deglaciation of central Lanarkshire. Scottish Journal of Geology. Vol. 5, 248–268. PATERSON, I B, MCADAM, A D and MACPHERSON, K A T. 1998. Geology of the Hamilton District. Memoir of the British Geological Survey, Sheet 23W (Scotland). ISBN 0 11 884533 0 ROSS, G. 1927. The superficial deposits in the Clyde Valley, 1.1/2 miles S. of Lanark. Summary of Progress of the Geological Survey of Great Britain and the Museum of Practical Geology for the year 1926, London, HMSO, p.158 -160. THOMAS, G S P and MONTAGUE, E. 1997. The morphology, stratigraphy and sedimentology of the Carstairs esker, Scotland, U.K. Quaternary Science Reviews, Vol. 16, 661–674.

Unpublished Documents PALMER, D C. 1975. Report on sites of geomorphological interest in Lanarkshire. Unpublished report for the Nature Conservancy Council and Lanark County Council. U’REN, G. 2015. The Falls of Clyde. Clydesdales Heritage. Unpublished book chapter. WIGNALL, R. 2008. Geodiversity of the Clyde Valley Woodlands. Unpublished SNH report.

Webpage links Lanark Hydros Technical Factsheet: http://www.spenergywholesale.com/userfiles/file/LanarkTechnical.pdf

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Shaping Our Landscape Geological Trail Report  

This report, published by British Geological Survey Scotland, is an assessment of geological sites in the Clyde and Avon Valleys. The geolog...

Shaping Our Landscape Geological Trail Report  

This report, published by British Geological Survey Scotland, is an assessment of geological sites in the Clyde and Avon Valleys. The geolog...

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