Physical aspects of Suffolk: Jurassic to Oligocene

TRANSACTIONS. PHYSICAL

ASPECTS

OF

SUFFOLK: i.

B Y FRANCIS ENGLEHEART, M . A . , B . S c . ,

F.G.S.

INTRODUCTION.—To most of us the geography of a region is something ineradicably fixed, at any rate uncil we stop to think.

T h e life of man, as we have been told, ' is as the flower of the grass' and, in the brevity of human affairs, the forms of land and sea, the pattern of the rivers and the uplands, and all the diversification of surface relief, seem to present a comfortable permanence, a strong perpetuation of the status q u o . — A n d yet a little thought, a little careful Observation will show this dream untrue. W e know about coastal erosion, the crumbling of the cliffs at D u n w i c h and elsewhere: sometimes we can even watch them crumble. Sands blow across fertile fields and may swallow up villages; lakes silt up, becoming swampy flats; mountain torrents may be thick and even thundrous with the very substance of the hüls, which thus is being steadily washed away. I myself have seen, in a few years only, a small river-island move several yards downstream.

When we turn our attention to the archives of the earth and learn to interpret somewhat of their fascinating story, we find in the crastal strata the records of geographies gone by. T h e gaps are many and mistakes o c c u r : we may not learn of these old conformations in meticulous detail, but we come to know something, because we can see what is happening today and often w h y lt happens, and can apply this knowledge to the p a s t ; for, though geographies change, the laws that produce them do not. T h u s we know it needs powerful currents to transport stones and gravel, which indicates shallow water near the shore, or beaches ; mud can be wafted farther in quieter d e e p s ; while limestone, though it may occur in-shore, can be fashioned in clear wide seas beyond the reach of the finest powdered washings from the land. W h e n Reposition takes place in the presence of currents the grains may be pushed over an advancing bank of sediment, so that the layers

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PHYSICAL ASPECTS OF

SUFFOLK.

lie tilted instead of horizontal, a condition known as false- or current-bedding. (This must not be confused with ordinary tilted bedding, which occurs on a larger scale and is produced quite differently.) A change in the current will slope a new series a different way, the resultant rock when sectioned showing a herring-bone effect characteristic of certain deposits such as the Crags. This teils of currents and so again shallow water. ' Ripple-mark,' often well preserved on ancient bedding planes, gives similar indications ; while ' rain pitting ' shows, of course, that the sand between tides was exposed to the air. In ways such as these we can get some idea of the face of the earth when younger.—VVhat we generally understand by geography, that of today, is then but a single snapshot of an endlessly changing scene : that is the leading idea we must make our own ; that gives us a sense of proportion.

T h e causes of these changes lie in several factors, the chief of which are those effects of crustal instability summarised as ' earth movements.' We have seen that in geology things mav not be what they seem. T h e phrase ' the eternal hills' is merely an extravagant hyperbole ; ' the solid earth ' is another misleading term. It seems rigid enough for such forces as we can command, but nevertheless it will bend and break to forces that there are.

A noticeable feature in large-scale movements is the rising of great areas of the floor of the sea to form land, perhaps swelling further into uplands, possibly crumpled into mountain chains.

Directly a land has emerged from the ssa the weather attacks it, the frost and the heat and the rain and the wind break it down, rivers wash it away to the sea, and the shore-waves wear it back : a general process known as denudation. This, if the lifting movement have ceased, may possibly be helped by a downward warp of the crust but, in the absence of any bodily movement of the rocks, denudation alone will finally obliterate the land : Nature wiping away her earlier work with a wash of the sea.

T w o special agents for altering geography may briefly be noticed.

Ice, whether polar or mountain, may bring about remarkable and characteristic changes, and, in the later centuries, man himsslf.— Ice sheets produce enormous torrent washes, and spreads of gravel, sand and boulder-clay ; glaciers gouge out corries and rock basins (which on the retreat of the ice hold lakes) and, when they melt, drop debris of all kinds to form moraines. Man as a moulder of the features of the earth has been comparatively weak ; he has reclaimed litoral marshes and even shallow seas and, on the other hand, made deserts in some places by forest destruction which tinds towards dessication and the washing away of the soil.

He is but the baby of the earth as yet, but what may he not do in the future ?—Thus not only is there change: there are regulär

PHYSICAL

ASPECTS OF

3

SUFFOLK.

cycles of change. Land rises from the sea, forms systems of rivers and possibly mountains, is glaciated perhaps, is eroded, and planed down once again by the sea. Nor is there merely one simple cycle, there are systems of cycles ; wheels as it were within wheels. The slow revolutions in this inorganic field are not unlike the rhythms of living things. There is youth, maturity, old age ; there are seasons of awakening and of sleep ; there is birth, there is death.

I t was the happy suggestion of the Editor that a series of outlines of the past geographies of Suffolk would be of interest and scientific use.

The PALAEOZOIC.—Before this Suffolk existed there were others, that is to say this area was land in several different epochs separated by p-nods of marine transgression. One cannot in this connection go back with any certainty before the Mesozoic but it is interesting to note the poseibilities of the Palaeozoic. The onlv rocks of this era which have been proved at depth within our district appear to be Silurian or oldcr. Imagination can thus run free on the succeeding epochs of this earliest of definite eras, since any of them may have found this part of the world above sea level A landscape of O I . D R E D SANDSTONE time would have contrasted strangely with that of today. It would have been a dry, hot, inhospitable land, possibly with bare Silurian rock or stony sand but, at least in the earlier part of the epoch, it would have been rock which echoed to no cry and sand that no foot stirred. For the earth of that far day had n o t ' brought forth the living creature after his kind': our picture must be void of all animal life, unless indeed its dessication was relieved by water. In the rivers, in those enormous lakes which lay to the north and west, or in the open sea which was somewhere to the south the waters had indeed 'brought forth abundantly', for this was 'the ageoffishes.'— Perhaps there was a CARBONIFEROUS County. I f so the scene was very different. I n a moist tropical heat enormous tree ferns spread their dripping fronds, and stränge uncouth Amphibians browsed on the smaller plants. In the swampy areas, now the coalfields and elsewhere, we know there were trees hke a monstrous overgrowth of the horse-tails of our damp places today, as well as and others l owards the end of the epoch vast earth movements began, and " is not improbable that these threw a mountain chain across our county, part of the vast ränge which undoubtedly extended from the south of Ireland into Russia. These heights had a similar ettect upon this country as that of the modern Himalayas on

(Calamites) (Equisetum) Lepidodendron, Sigillaria

tV i b y , C u t t l n S o f f w a t e r y w i n d s from the open sea to the south hey slowly made a desert of our a.ea, closing the e p o c h . - I n NEXT > T H E P E R M I A N , the giant club-mosses and

Sigillaria

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PHYSICAI. ASPECTS OF

SUFFOLK.

Lepidodendron still flourished in the damper parts, but generally both plants and animals were much impoverished. An inland sea of considerable size with a curious stunted fauna and waters heavy with calcium and magnesium laid down the Magnesian Limestone to the north and other depcsits. At this time a new kind of animal appeared : the reptile. Its early types, successful from the first, spread rapidly, and probably got on fairly well even in this dessicated county. There must have been much alteration in the geography of north-west Europe during this period and especially at its close, ushering in more faunal changes as the Palaezoic era passed into the Mesozoic.

About this Mesozoic we may speculate less and know more.

T h e T R I A S in this area saw a continuation of the Continental desert conditions but the climate was probably hotter. Red sand lay everywhere and blew about in storms, cutting and polishing such rocks as were exposed of which there may have been many, and finally forming part of the New Red Sandstone.

Life of all kinds was scarce, but in places a stunted Vegetation fed certain animals, notably reptiles and the characteribtic labyrinthodonts (amphibians with stränge teeth and curious hand-like feet) and a few small mammals, puny as yet and onlv potentially important.—Throughout the JURASSIC, a southern East Anglia was probably in existence; F.ast Suffolk and Essex were undoubtedly land in the Bathonian age of that epoch. When the Great Oolite limestone was being laid down farther west, a salient of land was probably centred roughly over Essex (possibly including the mouth of the Thames and Suffolk) and a clear sea lay to the west. Later large rivers north and south of this land opened into the western sea, bringing down masses of floating wood and sand or mud : the open water became less clear and not so d e e p ; and soon, in'a wide expansc of shifting shallows teeming with life, the F o r e s t ' Marble ' came into existence, a spread of current-bedded shell- and sandbanks, some of them dry at low tide. Between the rivers, the coastline (the East Anglian cape of the eastern land) ran somewhat from Yarmouth through Bury and Uxbridge to Canterbury.

T h e climate was damper : sub-tropical. Reptiles were now very much in the ascendent: on land huge saurians leapt on their prey, or browsed on the cycads and ferns. T h e r e were dragons that flew (pterodactyls) and much larger dragons (as Ceteosaurus) that wallowed and splashed in the marshes and estuarine flats.— When at the opening of the CRETACEOUS the land succumbed to the marine advances, a muddy sea deposited the Gault and later the U p p e r Greensand; a remarkable period then set in during which, over an enormous area, the soft white ooze of the chalk was laid down for a myriad years.

PHYSICAI. ASPECTS OF SUFFOLK.

5

At last, in the Cretaceo-Eocene interval, this part of the world rose and became dry land, a land it is hard to describe as scarcely a trace is left to teil the tale. We may picture a Suffolk of rolling Chalk and in its later periods strewn with flints, with lime-loving plants, very different from those of today. No doubt lizards and other reptiles, dinosaurs for example and the massive Iguanodon, roamed over the country, with snails hiding under the stones, and insects and other small fauna ; pterodactyls still flew in the air together with at least one genus of birds, Enaliornis.

There were molluscs in the rivers, Viviparus and other genera, as well as various fish and fresh-water reptiles. This raising of the Chalk was but an incident in one of the vastest convulsions the earth has known. Volcanoes in the Hebrides and elsewhere were pouring out floods of lava and, though nothing of this occurred here, the movements were very widespread. These geographical changes, made simultaneously over so much of the earth, brought about such alterations of climates and general conditions of life that the fauna of all this part of the globe took on new characters and became quite different. The great reptiles died out, their place being gradually taken on the land by such mammals as carnivores, ungulates and lemuroids, in the sea by whales and the like, and in the air by birds.

The change was complete: in England not one species persisted, except among foraminifera. Whole groups, as ammonites and belemnites, became extinct, and others arose, äs the snakes. Hence the name of the next epoch, Eocene (eos: dawn, kainos : recent), the dawn of recent life.—While these earth movements were working themselves out, the Suffolcian hills of Chalk were fast being worn away : some hundreds of feet were removed in the Sudbury area, and at last a sea which lay to the east and south cut back through the county.

For most of the EOCENE epoch, the first of the Tertiary era, this district was under the sea. At the time when the shore lay roughly between Southwold and Cläre, the fine Thanet Sands were being laid down in a sea of some depth in south-east Suffolk and beyond. The shore sank somewhat and the coast then ran from Lowestoft to Newmarket more or less, but the sea on the whole was shallower. A large river debouched south of London depositing mottled clays and coloured sands throughout the area : the Reading Beds. There were few shells, and no doubt the water was brackish ; in it were sharks and teleostean fishes, also tortoise and turtle and crocodile. The climate was temperate : plants like Laurus and Platanus flourished on the land.—As time went by the deposits being brought down changed and became more muddy, and the London Clay was laid out in a sea of no great depth containing shells of genera (though not species) iamiiiar to us today, together with crabs, fish and turtles

BITTERNS

AT

LOWESTOKT.

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PHYSICAL

ASPECTS OF SUFFOLK.

In a subtropical climate palms grew on the coast with figs, sequoias and magnolias.

T h e sea covered most of Suffolk and extended to northern France.

After long ages, in the OLIGOCENE epoch, the sea floor rose again ; land stretched from Ireland to north Germany. Over this there wandered mammals, such as Hyopotamus and Palaotherium, in a landscape very different from any that had gone before, since, in addition to other plants of which we may name Sequoia and Osmunda, there was grass, which sheltered snails and insects and the like. It is hard to over-estimate the debt we owe to the grasses on which almost all modern animals and all mankind depend. Denudation continued its work, and much of the Oligocene land (made of Eocene material) was worn off. T h e climate grew somewhat colder as Oligocene passed into MIOCENE.—All about this time, for many millennia, the world was undergoing a seismic and volcanic revolution of such a vast and thorough-going type that mountains were crushed up all round the earth : the Alps and Himalayas are legacies of those days. Suffolk however was in a quiet area and, although on a map it would have been quite unrecognisable, there were certain similarities with the conformation today. A North Sea was formed, somewhat east of the present. There was even an Aide, a Deben, a Gipping and a Stour, which were the vague beginnings of those we know.—Finally a new subsidence occurred and the sea ran in, probably forming the ' Coprolite Bed ' at the base of the Crags with its ear bones of Whales and other remains now black and phosphatised.

ON

THE

LOCAL

BY T .

NIOBE

NAUNTON

BUTTERFLY.

WALLER.

IT has been suggested to me as desirable that, in view of the forthcoming detailed Catalogue of Suffolk Lepidoptera that our Society proposes to issue, I should State the facts of my " beginner's l u c k " in having possessed the sole example of Argynnis Niobe, Linn., found in Britain throughout the whole of last Century. For this purpose it is essential to wax personal: I was born in 1863 ; and in 1876 my late father, the Revd. T . H .

Waller of Waldringfield near Woodbridge, sent me to King Edward vi's Grammar School in Bury St. Edmunds, then under the headmastership of the Revd. A. H . Wratislaw, M.A. (Trans, ii, p. 64), father of our present Member A. C. Wratislaw, C.B., C.M.G., etc. Occasionally the Head, who was very keen on