TRANSACTIONS
OF THE
GEOLOGICAL
SOCIETY
CHAPTERS IN THE GEOLOGICAL HISTORY OF EAST YORKSHIRE."
Given by MR. ALFRED HARKER, M.A., F.G.S., Demonstrator in Geology in the University of Cambridge, to the Members of the Hull Geological Society, January 9th, 1890.
(Included in these Transactions on account of its local interest)
Mr. Harker said that the neighbourhood of Hull is shrouded with a thick mantle of Drift and other deposits. The Wolds and the district to the West of them, though presenting varied strata, do not afford a complete succession, and are less known than they deserve; therefore the lecturer included the N. E. moorlands and the section of the York- shire coast, which has been made classic by some of the greatest English geologists, besides many other workers past and present. It was almost inevitable that the earlier portions of any history should be involved in darkness; if true of human histories, the geologist finds it forcibly brought home to him by the varied story of the earth itself. The changes are foreshadowed to the geologist in the preceding chapters of the record. We are learning that Evolution, originally initiated for the organic world, will supply the clue to the development of the physical features of the globe, and within the last few years striking results have been obtained by applying this key to geological problems. We must proceed by observation. The reconstruction of the earth's history and the arrangement of the various episodes in their proper relations as parts of a whole are tim great aim of geology. This branch of geology is in its infancy: only a few of its generalisations can be placed among established facts. Material which only careful local work can supply must be amassed before the complete history of any part of the earth can be made clear. This is especially true of the older rocks, the Primary or Palaeozoic, the first volume of the record of the rocks. Fifty years ago these were looked upon as a hopeless and chaotic residuum, but an enormous amount of information has been collected by the energy of a limited number of workers. In East Yorkshire no Palaeozoic rocks are exposed at the surface, but there could be no doubt during the oldest known period of organic life (the Cambrian) the district was submerged beneath the ocean, which extended westward from Russia far across the Atlantic, and continued into the Ordovician period, which was a time of disturbance in the earth's crust. The Lake District was flooded with lava. Whether East Yorkshire was upheaved at this era or at the close of the Silurian he could not say, but it may have shared the continental conditions prevailing over the British Isles during Devonian times, when our district was probably a large lake. Passing to the Carboniferous period, the evidence of surrounding districts suggested that during the Mountain Limestone age this district was a tropical sea studded with coral reefs, while a further re-arrangement gave rise in Coal Measure times to alternating estuarine, fluviatile, and terrestrial conditions, and coal was then formed in this neighbourhood. The Permian in England was a period of disturbance. The Coal Measures which crossed England were then folded into basins divided by elevated ridges which were denuded, and the back-bone of England then came into being -- the Pennine mountain-chain which, with other ridges, cut off from the ocean a large inland sea to the eastward, in which the Permian deposits of Yorkshire and Nottinghamshire were laid down. Our district then formed part of a sea like the Caspian, and some geologists say there is evidence that the mountains formed the gathering-ground for considerable glaciers. The deposits formed in this sea were, first, red sandstone, then magnesian limestone and gypseous marls to 600 or 700 feet thick, and the conditions were not favourable to animal life, but such as are found have Palaeozoic affinities. With the continental conditions of the Permian period it might be considered the Primary epoch came to a close.
Turning to the next volume of the record of the rocks -- the Secondary or Mesozoic epoch -- the lecturer pictured the conditions subsisting in that long bye-gone time. There was no definite land-area which could be pointed out as Yorkshire; only some of the European Continent had been marked out. The Alps and the associated chains did not arise until long afterwards; the Mediterranean Sea covered much of the south central regions; a range from Poland into France, of which there are still relics, then stretched through Brittany into the Atlantic, meeting the Scandinavian chain. This enclosure affords the key to the nature of the rocks then accumulated. These rocks (the Triassic) exist and are exposed in East Yorkshire. They introduced a new order of things: the upheaval was stayed and depression succeeded. The depression is marked by the marls of the Upper Trias following the sandstones of the Lower. The English Trias as a whole points to peculiar physical conditions, analogous to those now found in parts of Central Asia. The region was divided from the ocean by lofty mountain- ranges, which cut off the ordinary supply of atmospheric moisture and produced a desert-like climate. The dryness of the atmosphere gave .rise to rapid evaporation; hence the deposits of salt and gypsum and the formation of iron-compounds which stain the Lower Triassic deposits. Fossils are not common in the Trias of England, but from other parts of Europe evidence is obtained shewing marked change in the Life-forms. The old crustacea, brachiopods and mollusca had disappeared. New forms of fishes had appeared, and remarkable reptiles, and near the summit of the Triassic formation remains of the earliest known mammal have been found. The Rhaetic beds are observable at several places in Yorkshire though now missing in some places.
The northern half of the Yorkshire coast presents continuous sections of the Jurassic strata, both Lias and Oolites, scarcely excelled by any others in the world. The lower divisions of the Jurassic, the Lias, consists of a thick series of clays and shales, argillaceous limestones, and ironstones, in frequent alternations, the clayey strata predominating and richly fossiliferous. The argillaceous beds give evidence of broad and deep seas receiving sediments, while limestones tell of waters purer but shallower. The alternation of different lithological deposits is proof of change of elevation and subsidence in the sea-bottom. The ironstones of the Middle Lias have made Cleveland famous. Their origin has probably been as Dr. Sorby has suggested; the rock was originally limestone, often with an oolitic structure, and the replacement of the carbonate of lime by carbonate of iron, and of the latter in part by oxide of iron, has been a later process. Excepting only the Mammals, almost every existing Order of the Animal Kingdom fund its representatives in the Liassic seas. The climate in these latitudes was warm and equable, and it continued so throughout the time during which the succeeding Oolitic strata were formed. In the South West of England there is evidence of deposition in an open sea, but in the North East we find the marine Liassic strata succeeded by beds of estuarine origin. The Yorkshire Oolites tell of intervals wherein the area was covered by the sea, but the great mass of strata consists of barren shales and strongly current-bedded sandstones formed only by some great river, and the nearness to land is proved by vegetable remains : Cycads, tree-ferns, and giant equisetums were conspicuous in this Oolitic flora, and Gristhorpe near Scarborough is famous for its finds. The estuarine conditions were best marked in the coast district. At Cave the most important deposit of the Oolitic age is that representing the chief marine phase of that time in North England, viz., the Millipore Oolite. This consists of impure oolitic limestone, which seems to have been deposited in a sea extending southward through Lincolnshire and Rutland, having its northern limit at the Tees. The succeeding Kellaways Rock -- an irony and calcareous shallow-water sandstone with abundant fossils -- is almost absent in Central England, though well represented in Wilts and adjacent counties. The Oxford Clay at Cave is a dark blue tenacious clay; its representative at Scarborough and in North East Yorkshire is a shale of a sandy nature, which indicates that in the last named district we are approaching the limit of the sea in which the Oxford Clay was deposited. The upper part of the Middle Oolite would repay investigation. The purity of some of the limestones and the profusion of reef- building corals prove that during part of the time our district was far removed from any land to contribute much detritus to the sea. The absence of Corallian rocks South of Acklam must not be left out in attempting to restore the physical features of the age. In Lincolnshire they are wanting. An argillaceous deposit was characteristic of the Kimmeridgian sea from Yorkshire to Dorset. The life of the Jurassic period shews a correspondence with that of Australasia, though all the species, and in the higher Orders the genera too, of the Jurassic are extinct. The Jurassic had been designated the "Age of Reptiles." The close of the Jurassic was marked by movements of elevation in the British area. The unconformity at the base of the Cretaceous formations is one of the striking features of East Yorkshire. During the earlier part of the Cretaceous period much of England was above water, as is proved by the Wealden deposits, which are followed in the South of England by the lower Greenland. Neither extended into Yorkshire, and during their formation our neighbourhood was terra firma. The Speeton deposits must have been then forming in an open sea; meanwhile the tract above water was being denuded, until the Oolite and Lias were bared. In the general submergence this surface was covered, and became the floor on which the Upper Cretaceous rocks were laid down. The result is the unconformity of the Yorkshire Chalk on the Lower Lias. It is less marked eastward, and in Mr. Lamplugh's opinion it dies away before reaching the present coast-line. If so, the Speeton district was unaffected by the elevation and subsidence described, and an unbroken series of marine deposits was being formed there from the Middle Oolites up into the Middle Chalk. The sea in which the Chalk was formed, though not deep, was extensive; it must have covered the United Kingdom besides a large part of Europe. The resemblance of the deposit to the calcareous "ooze" of modern oceans has apparently been exaggerated. The climate appears to have been temperate. With the Cretaceous many life-forms disappeared After the Cretaceous in the geological history of Yorkshire a long succession of ages is unrepresented by any sedimentary formations. The break between the Chalk and the overlying Tertiary strata in the South is shewn by a marked unconformity of the latter upon the former. In Yorkshire the gap is far greater, the whole of the Tertiaries being absent, and there is no evidence they ever existed here. The Tertiary period largely developed the present relief of the earth's surface. We owe to it the greatest mountain-ranges of the world. Enormous masses of rock have been removed by destructive agencies from the Yorkshire area since the deposition of the Chalk, and the greatest part of this denudation took place before the Great Ice Age, and so during the Tertiary period. The land doubtless rose gradually; there was a gentle slope to the East which probably determined the direction of flow of the Humber, which then originated. The sea had formed a line of cliffs to the East, not corresponding with the coast-line of to-day. After long denudation the out-crops of the Middle and Lower Chalk were left standing out as an escarpment, now known as the Wolds. To the West of this not only was the Chalk removed but the underlying formations underwent great denudation, so that beyond stretched a plain of Triassic rocks. In North Eastern Yorkshire the directions of drainage and other features have been determined by foldings of the strata which may be connected with the great Alpine system of earth movements; they may have begun to be formed at an earlier time. The contortions of the Chalk strata at Staple Nook to the north of Flamborough may be referred here. To this epoch too we may assign the formation of the broad and shallow synclinal basin of Holderness including North East Lincolnshire, where a depression of the solid strata took place, leaving as denudation progressed the soft and flintless Upper Chalk surrounded in a semicircle by the Middle and Lower Chalk; upon the open side of this the sea encroached westward, so that a bay was formed, the site of Holderness and a part of Lincolnshire. The northern limit thereof was not far from Flamborough Head; from there the line of cliffs ran by Bridlington, Driffield, Beverley, and Cottingham, to Hessle, on the Humber. On the other side thereof the cliffs turned south easterly by Thornton, Ulceby, Keelby, Laceby, Hawerby, and Sudborough. Its limits can be traced by a sharp rise of the Chalk beneath the later Boulder Clay, and a portion of the old cliff itself with the talus and beach has been laid bare at Sewerby near Bridlington. To the Tertiary period belongs thus the first sketching out of Holderness. The Tertiary period was a time of great igneous activity, and various places where active volcanoes then existed were referred to. The chief emissions of volcanic material were effected by great fissures through which lava welled up: these are in evidence in the long straight dykes of igneous rock. The Cleveland dyke enters East Yorkshire; it runs from the neighbourhood of Whitby to near Carlisle, 110 miles, and possibly to Ayr, 80 miles further. We may therefore boast of one Tertiary rock in Yorkshire. The Cleveland dyke is the only igneous rock in the East of the county. The Tertiary strata of the South of England and the Continent afford an interesting study of life-history; the fossils there record the dawn of species now living with the extinction of obsolete forms. Here that record is wanting. The succeeding Glacial epoch extends the gap. We have little between the Cretaceous fauna and flora and those of Post-Glacial and Recent times. At the close of the Tertiary period the condition of East Yorkshire would be much the same as now. The Vale of Picketing had come into existence in Tertiary times; its waters probably drained not westward but eastward into Filey Bay. The coast- line to the north must have stood east of its present position, and the bay possibly extended farther into the country and received one or more streams. The Chalk rose as at present, and Flamborough Head stood farther out to sea. From this cape the Bay of Holderness extended in a long curve, receiving the Humber Estuary at Hessle. It is by no means improbable that glacial conditions prevailed at more than one earlier epoch, but they have left few traces which have survived the vicissitudes of denudation. The Post-Tertiary Ice Age has given us many smaller and some of the larger superficial features of the country, and evidences thereof are written in lake and valley, on mountain and plain, throughout the country. With the causes of the Glacial climate we are not concerned. The successive faunas of the English Tertiary prove a gradual lowering of mean temperature, and upon its close the northern regions of America, Asia and Europe, including the British Isles, were subjected to climatic conditions similar to those of Greenland, parts were covered by ice for long ages, seas were filled with icebergs, and their floors were covered with the debris dropped from them. In Northern Europe, and indeed in northern Britain, there is proof of great ice-sheets covering high land, sliding towards the sea regardless of minor elevations and valleys, and at their margin sending out tongue-like glaciers into the lowlands or to the sea. The grooves and scratches on the rocks by the ice, and the vast volumes of mud ground by the ice-sheet, prove that ice over-rode some of our own mountains, and enable us to distinguish several local centres of glaciation. The Glacial epoch includes two, or more than two, periods of glaciation, separated by intervals of milder conditions. The first glaciation was the most important one, and the extensive Boulder Clays belong to this date, including the Basement Boulder Clay of Holderness, which is covered by the later "Purple Boulder Clay." Holderness occupied a peculiar position during the Glacial epoch. The Scandinavian mountains formed the gathering ground for enormous ice-sheets, a branch of which ice filled the North Sea, met the Yorkshire coast, and was thrust into the Bay of Holderness. The foreign origin of parts of the East Yorkshire Boulder Clay is attested by boulders of recognisable Norwegian rocks. This Scandinavian ice-sheet bore back the ice streams of British origin. The great ice-sheet of the North of England, due to the coalescence of the Scotch with the Lake District ice, sent long glaciers down the main Yorkshire valleys, which reached the coast and were stopped by the Norwegian ice-sheet, depositing their mud and variously derived boulders. The intermingling of the materials affords a problem yet to be solved. The boulders in the Basement Clay include rocks from Norway, the Scottish Uplands, the Cheviots, and possibly the English Lake District, in addition to those of more local origin, those forced up from the sea bottom, and large masses transported from one part of the coast to another. The story o the Glacial Epoch is told in Mr. Clement Reid's memoir on Holderness. Of an Interglacial time Britain has only scanty traces, and perhaps no evidence of more than one. The chief Interglacial accumulations in Holderness are a set of marine gravels skirting the old coast-line. The re-elevation of the land was accompanied by the refrigeration of the climate. The main Purple Boulder Clay of Holderness was now produced, Lake District rocks are not uncommon in the Purple Boulder Clay, granite of Shap Fell and the Permian "brockram" of the Eden valley being conspicuous. An amelioration of the climate caused the retreat of the ice, and erratics and perched blocks remain. There is reason to believe that after the Glacial Epoch the British Isles had a more extensive area than now: and were joined to the Continent. The bulk of the morainic material was massed, with the products of British glaciers, in the neighbourhood of the old shore line and the tracts adjoining. The old Bay of Holderness had been filled up with Boulder Clay. The mouth of the old Filey Bay, the seaward opening of an extensive plain, had been blocked, and thenceforth the Vale of Picketing drained westward through the Malton gorge. The streams rising close to the present cliffs between Hornsea and Spurn flow not into the sea but south-west into the Hull and the Humber. At this time Britain was an integral part of Europe. The Humber, Thames, and other streams flowed into a larger river running northward in the mid-channel of our North Sea. It is not unlikely that the later phases of the Ice Age in England may have been witnessed by human eyes. The history following the Glacial Epoch is obscure. The earliest Post-Glacial deposits in East Yorkshire indicate that the land stood 40 feet lower than now. This is proved by a raised beach at Saltburn. An elevation succeeded this. The North Sea may have been dry land. The depression has left traces in the "submerged forests" of this neighbourhood. The life of that age, as preserved in the “buried forests" and in lacustrine deposits, indicate a mild climate. The Lion and Hyena lived at Hornsea, with the Horse, Red Deer, and Irish Elk; also the Mammoth and Bos primigenius. In the lower buried forest at Hull traces of a fire present the earliest evidence of Palaeolithic man in this neighbourhood. The depression of the land to its present level brought a new phase in the history of Holderness. While at a higher level erosion had cut valleys in the Boulder Clay; when subsidence ensued they were converted into salt-water creeks, which gave rise to the meres. An immense number of these lakes are traced in Holderness. The one at Hornsea is the last survivor, and the silting up of it and the sections in the cliffs show how the lower ground of Holderness has been filled up. It is also evident that this change operated since the district has been tenanted by man. Mr. Harker referred to the discovery of the old pile-dwellings at Ulrome, which resemble those of Switzerland, and to Mr. Boynton's excavations carried on there. The original district was more extensive than the Holderness of to-day. The coast-line appears to be receding at present 2 1/2 yards per annum. When the Roman legions encamped in this district, the shores of Holderness were two or three miles further eastward, and many villages have disappeared beneath the waves. Spurn Point presents a curious geological and hydro-mechanical problem, owing its existence and preservation to an ever changing equilibrium between the action of the sea on one side and the Humber on the other. It is a bank of shingle and sand, the Boulder Clay ceasing at Kilnsea Warren: the spit of shingle is three miles long. Three centuries ago the point had no existence; it has extended southward, and is extending 13 1/2 yards per annum. If left to itself it would extend southward until the river broke through. If the history of Holderness is one of destruction and loss, the reclaimed lands of the Humber Estuary present a partial compensation. Of the 6,000,000 tons of material annually removed from the sea-coast, the coarser portions form the banks of sand and shingle which block the Humber and the North Sea and the dunes which cover Spurn Point and some parts of the Lincolnshire coast. The fine mud remains suspended and travels long distances, and large quantities of “warp" are deposited. Sunk Island has been so formed: it began to form in the time of Charles I. Its area is now about 700 acres, and, including adjacent reclaimed lands, Mr. Oldham calculated that the total gain between Paull and Spurn from 1684 to 1850 was about 10,000 acres of rich land. Mr. Harker concluded his able paper by stating that it was impossible to follow the changes in the channel of the Humber even in historical times, and that the history of the lost towns of Ravenser and Ravenserodd was still obscure.
[Note -This article has been scanned in from original printed format and then put through an OCR program by Mike Horne. The process may have introduced some new spelling errors to the texts. Some original misspellings have been corrected.]
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