A Contribution to the Geological History of Suffolk, Supplement

A CONTRIBUTION TO THE GEOLOGICAL HISTORY OF SUFFOLK Supplement Eocene

HAROLD E . P . SPENCER, F.G.S.

COASTAL erosion along the left bank of the estuaries of the Orwell and Stour continues to attack the London Clay but with little addition to our knowledge so far as the Orwell is concerned. At Harkstead Cliff, on the east side of Holbrook Bay, it has been severe at the southern end. Formerly, the whole cliff appeared to be London Clay with small inclusions of gravel at intervals near the top. These were interpreted as being the stony margin of the Stutton Brickearth forced by the pressure of freezing into the clay, this being a phenomenon of the last glaciation since the fossil evidence and flint artifacts prove the Brickearth to have been deposited during the last, Ipswichian, interglacial. Other evidence of this pressure has been noted in the Wrabness Cliff on the opposite shore. Mammalian bones in a crushed condition have been observed in the Brickearth, the crushing being obviously due to pressure against the resistance of the London Clay. The erosion occurs mainly when the wind blows from a westerly direction and particularly when it is from the direction of Jacques Bay when the gales have two and a half miles in which to build up waves.

Some years ago Mr. F. W. Simpson discovered some poorly preserved molluscan fossils at the foot of the London Clay cliff at Harkstead which have not been identified. These are preserved in the local museum, they are worthy of note because fossils of any kind appear to be of exceptional rarity in Suffolk London Clay.

Upper Pleistocene—Late Ipswichian Excavations for gravel have been made in the flood piain gravels of the River Gipping opposite the Sugar Beet Factory at Sproughton, in the area enclosed by the Chantry Reach and the cut made when the river was canalised early in the last Century.

These excavations have enabled an examination of the nature of the deposits formed in an "Ox-bow" made when the river flowed much more rapidly and with a far greater amount of water than at present. Fossil remains of reindeer, Rangifer tarandus, are an indication that the climate was cooler and more akin to that of Northern Europe of the present day.

Wartime dredgings from the river bed yielded other bones, including Bos primigenius and notably Iarge numbers of shells of a large variety of walnut which presumably was growing in the Gipping Valley when the deposits were laid down. No walnut shells have so far been observed from the flood piain deposits.

518

Suffolk Natural History, Vol. 15, Part 6

Below the flood piain gravels there is a brown laminated argillaceous deposit containing numerous leaves of willow. Dr. Charles Turner has taken a quantity of this bed for examination and in due course his report will reveal what other interesting items may be included.

Above the laminated clay are sands and gravels, some of these have highly inclined bedding, in general they are complex such as would be expected where rapidly flowing water was removing the bank on the outside of a meander and depositing debris on the opposite lee, see FIG. 33 A and B. In this way "Ox-bow" lakes are

Part of the River Gipping, below Sproughton, showing the Chantry Reach and the cut made when the river was canalised.

FIG. 33B

Illustrating the work of a river and the formation of meanders which sometimes result in the formation of an Ox-bow Lake.

GEOLOGICAL HISTORY

519

formed by the old Channel and the river takes a new circuitous course, the old Channel eventually becoming filled with marsh deposits.

T h e gravel and sands are sealed below thick marsh deposits containing roots and pieces of wood with occasional incomplete bones of post-glacial animals. It is not clear why no complete bones have been noted, but, as large numbers of waste flakes of flint left by prehistoric hunters have been found between the river and the Sproughton Road as well as dredged from the river bed, it is perhaps possible they may have been responsible.

Former gravel workings at Bramford Road, Ipswich, and near Hadleigh Road, which brought up bones with the gravel from well below the water table, a lower level than the Chantry Reach site, yielded remains of Mammoth and Woolly Rhinoceros in addition to Reindeer.

T h e marsh deposits vary in thickness from about five feet to about eight feet and as usual are black while damp but dry to grey, sometimes with an efflorescence. At this site the dry surface has brown patches due to an hydroxide of iron, also a blue powdery efflorescence of Vivianite, hydrous phosphate of iron, which often occurs where organic matter such as bones and iron are present. T h e ground water which is pumped from the excavation and drains from the gravel is brown due to the presence of iron.

Bosmere Excavations for a fish pond near Bosmere Water Mill in the Gipping gravels have yielded a femur, a humerus, and an incomplete ulna of the Woolly Rhinoceros, Coelodonta tichorhinus, from below the water table. It is easy to assume that the bones may belong to one animal but if a skeleton were present some vertebrae or pieces of ribs ought to have been brought up also. T h e staff working on the site are keenly interested and will preserve any further bones which may be found.

Similar bones from Barham some two miles downstream were associated with Hyaena (who had gnawed some of the rhino' bones) Tiger, Wild Ox, Horse and Reindeer, also Wolf.

Early Pleistocene A new pit in the Red Crag has been made recently with over ten feet of this uniquely East Anglian deposit exposed. It is close to the Marina at Stratton Hall. T h e slumping in the western section is probably due to its proximity to the adjacent cliff, near Levington Creek.

H. E. P. Spencer, F.G.S., 43 Benacre Road, Ipswich,

Suffolk.