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EAST YORKSHIRE FIELD STUDIES

Number 2

first published 1969

An Introduction to the Geology of Holderness with Special Reference to the Coast

By K. Fenton

Note about the "Hessle Till" (Mike Horne 2012)

The Chalk of the Wolds extends in an arc from Flam- borough Head to the Humber and dips down beneath Holderness so that its surface is about too ft. below sea- level around Kilnsea. Post-Glacial alluvium flanks the Humber and spreads out over the River Hull valley, but the principal deposit in Holderness is the material left behind by the extensive Pleistocene ice-sheets which covered north-west Europe. This extends from the eastern flanks of the Wolds to the eroding coast where it provides the characteristic hummocky landscape. Around Brandes- burton, Burstwick and elsewhere are masses of sand and gravel but most of the glacial deposits are boulder clay or 'till'. This consists of a clayey matrix in which is present a variety of rock fragments from the size of small pebbles to boulders a few feet across. All this material, the unsorted till and water-sorted silts, sands and gravels, was originally transported into the area by moving ice which then melted leaving its load of debris as evidence of its presence.

On a world-wide scale the geological evidence of the events of the last one to two million years indicates a series of climatic fluctuations of which in Britain the last three major cold periods (see Table 2) or 'Glacials' with intervening temperate periods or 'Interglacials' are well represented, with evidence, in places, of some of the earlier parts of the Pleistocene succession. The causes of these fluctuations still remain as matters for speculation. It is also uncertain whether or not they have ceased so that prevailing conditions may perhaps be only another interglacial period. The principal areas of accumulation from which the ice, because of its ability to flow, has travelled to Holderness are Scandinavia, Scotland and the Borders, the Lake District and parts of the Pennines. This can be deduced from the various kinds of 'erratic' rocks present in the glacial deposits, although, for the beginner, many of these are difficult to identify. The most important indicators are those rocks whose place of origin is a known, restricted area. Such examples are larvikite and rhomb-porphyry from Scandinavia, jasper from Scotland, Shap granite from the Lake District and Brockram from the Vale of Eden. Widely distributed rocks with extensive outcrops give less exact information particularly as many of them may also crop out on the bed of the North Sea. Such less exact indicators include Carboniferous and Magnesian limestones, basalts, dolerites, Triassic sandstones and a wide variety of Mesozoic rocks. Some, such as black flints, are not derived from any known exposures and must, therefore, have originated from under-water outcrops. A better knowledge of North Sea geology will help to elucidate some of these problems.

Soft clays and sands were rapidly digested within the mass of moving ice and debris and so are unusual as erratics, but apart from these there is a wide variety of rock-types which can be found within the deposits or washed out on the beaches. Igneous rocks include many kinds, varying from coarsely crystalline granites to porphyritic dyke rocks, vein quartz and finely grained dolerites and basalts. Metamorphic rocks are represented by gneisses and schists, and sedimentary rocks by various sandstones, limestones and shales, septaria, pyrites, coal fragments, etc., (waterworn fragments of concrete, brick and glass on the beach may puzzle the beginner). Derived fossils, (i.e., ones picked up as erratics from older rocks) are very common, the most obvious being corals such as Lithostrotion from the Carboniferous, the nearly indestructible Gryphaea, masses of 'shelly limestone' and ammonites from the Lias, and belemnites and echinoids from Cretaceous beds. The boulder clay or till is not a uniform mass. Along the coast several distinct beds can be seen in the cliffs and on the foreshore when, as occasionally happens, the sand is removed by the action of the sea. Inland, apart from the surface layers, exposures are rare and it is most regrettable that borings and excavations have not been recorded in critical detail. At present four beds are recognised and all of them can be seen at Dimlington where the cliffs exceed too ft. in height. The sequence as seen above beach level is shown in Table 1 and Fig. 1. The nomenclature used is that of Catt and Penny and differs in some details from that used in earlier descriptions.

Table i

Name of Till	Approx. thickness	Dominant colour of matrix
Hessle	5-15 ft.	Foxy-red, sometimes yellowish
Purple	20-60 ft.	Dark reddish brown
Drab	20-30 ft	Dark chocolate brown
Basement	0-10 ft.	Grey-brown, distinct greenish tinge.

Around Withernsea the cliffs are much lower and only Purple and Hessle tills are visible, but between Aldborough and Hornsea Drab till appears again in the cliffs beneath the two upper tills. There is a characteristic 'red-band' within the Drab till which occurs just above beach level. A re-appraisal of the relationship and extent of the Purple and Hessle tills seems to be desirable in this area. North of Hornsea the cliffs appear to contain only representatives of the Drab till and the upper few feet have weathered to a brown colour with the fissures turning blue-grey similar to the Hessle till in the south. That this coloration is the result of weathering further strengthens the necessity of re-assessing the distribution of the Purple and Hessle tills, the latter being perhaps more of a weathering phenomenon than a true bed of till. Most of the Drab till in the high cliffs to the north of Hornsea has a distinctly Drab-coloured matrix but in texture and the small size of the erratics is curiously different from that south of Hornsea. In one short stretch between Atwick and Barmston, however, the texture and red-band characteristic of the Mappleton area reappears. Here erratics are large and many of them are strewn on the beach clearly marking the regional difference. Towards Barmston the till occupies only the lower part of the cliff and disappears beneath the beach altogether around Fraisthorpe. The upper part of these low cliffs and the entire cliff from Fraisthorpe to Bridlington promenade appears to consist, where not overgrown, of a mixture of distinctly varved clays, banded silts, sands and gravels so that all this northern part of the cliff could well be described as a predominantly melt- water area in marked contrast to the tills of the southern part of the Holderness coast. At Bridlington the cliffs, which were originally described in the last century, are now covered by, the promenade. Occasionally, after scouring has cleared away sand from parts of the north beach, Basement till can be seen. From the promenade towards Sewerby, Drab till occupies the cliff face except for the top few feet of Sewerby gravels. These two beds extend over the chalk when it appears in the cliffs.

Erratic rocks are present throughout the four beds of till. Many show so-called 'ice-scratching' where they have been in contact with other hard material during transport. Generally when elongated rocks are examined in situ they are found to be preferentially orientated with their long axes parallel to the direction of the flow of the ice. This is approximately from the north-east in Holderness. The distribution of the various kinds of erratics in the four different tills is not uniform and a careful re-assessment of the suites of erratics may well be a major factor in constructing a satisfactory model of the ice-sheets which have covered Holderness. Scandinavian erratics are most abundant in the Basement till with some Chalk, black flint and Magnesian Limestone. Drab till is characterised by an abundance of Chalk and flint with granites, Carboniferous Limestone, Border and Scottish rocks. Scandinavian erratics become infrequent in the higher parts. There is still Chalk present in the Purple till as well as Border rocks but in the Hessle Till erratics are both smaller and fewer in number. The distribution of the tills inland is difficult to ascertain. Certainly in south Holderness and extending to the flanks of the Wolds Hessle till appears to provide a surface covering but a great deal needs to be known about the extent of all the tills.

I

In order to analyse the relationship of the Holderness tills to the glacial sequence observable elsewhere it is important to look for both key statigraphical evidence and any fossil remains of plants and animals. The latter in particular may provide decisive dates. As so much is hidden, particularly along the coast where there are some 100 ft. of deposits between beach level and the surface of the Chalk, are there any other deposits beneath the Basement till? Such evidence as exists indicates that none are present although the question should still be considered an open one. On the other hand, bearing in mind the maximum southerly extent of ice-sheets, pockets of quartzite pebbles found around 4-500 ft. on the high Wolds have been interpreted as remnants of an earlier glacial coverage since removed by erosion. To turn to more concrete evidence there is a 'buried cliff' which exists on the eastern side of the Wolds and extends from Sewerby via Driffield, Beverley, and Cottingham to Hessle. This was exposed in Hessle Station Yard over half a century ago and is now overgrown. At Sewerby its presence is marked by the sudden appearance of Chalk in the lower half of the cliff. Its detailed features are normally obscured by slippage. Rarely, as after the 1953 storm surge, the old beach is visible but most of our information on this site is derived from excavations carried out in the 1880's and shown in Fig. 2. The old beach with its waterworn pebbles is slightly higher than the present one. It is covered by land wash and then an extensive layer of blown sand capped by chalk rubble. Drab till covers this rubble and the top of the cliff is composed of the Sewerby gravels. The rubble, Drab clay and gravels continue over the Chalk. Some fossil remains were found in the beach shingle, land wash and blown sand including Palaeoloxodon [Elephas] antiquus (straight- tusked elephant), Hippopotamus amphibius, Didermocerus hemitoechus (narrow-nosed rhinoceros), and a vole, Arvicola terrestris. These must have lived in the area during an interglacial period.

About a century ago, prior to the building of the promenade at Bridlington, masses of greenish sand containing glauconite and a very large number of fossil shells were discovered and designated as 'Bridlington Crag'. On a few occasions since, when the sea has removed the beach sand adjacent to the 'Pavilion', other patches of 'Crag' have been exposed, as well as some blue clay. The last time was in 1964. This material, being enclosed within the Basement till, apparently represents 'erratic' portions of an earlier North Sea floor. Numerous foraminifera and ostracoda can be isolated from the 'Crag' by sieving. The many mollusca include species of Dentalium, Macoma, Cyprina, Mya, Nucula and Venus. Within the Basement till at Dimlington are patches of bluish clay which, although the number of species is fewer, contain a similar suite of fossils. This has been referred to as 'Sub-Basement Clay' but, in spite of the difference in matrices, it is difficult to do other than interpret this material as being contemporaneous with the 'Bridlington Crag' and similarly derived from an old North Sea floor. Small Scandinavian erratics found in the blue clay may have been dropped from floating ice prior to the advance of the ice-sheets which formed the Basement till. These fossils at Bridlington and Dimlington belong to an interglacial period but the present distribution of the species involved is a northern one so that the interglacial climate must have been colder than it is now. Bedded silts occur in small basins at the top of the Basement till at Dimlington. About twenty-five years ago some fresh-water remains were first recorded from one of these basins and others have since been discovered. They consist of the shells of ostracods and fragments of a moss, Hypnum. These pools must have existed in ice-free conditions after the deposition of the Basement till and before the advance of the ice-sheet carrying the Drab till. Within the upper beds of till, that is the Drab, Purple and Hessle tills, occasional fossils of significance are found, in particular remains of the mammoth, Mammuthus [Elephas] primigenius. Most problematical of all, however, are the fossiliferous gravels of Burstwick and Keyingham which are at present being worked, and the now overgrown pits at Boreas Hill, Paull, all presumably a connected series of deposits. Various vertebrate remains from the Burstwick and Keyingham pits include Mammuthus [Elephas] primigenius, Rhinoceros, Bison, Odobenus rosmarus (walrus), Cervus elephas and Rangifera tarandus, there was also a fragment of a molar of Palaeoloxodon [Elephas] antiquus. The many marine mollusca present are indicative of a climate similar to our own and of shallow water. Examples are Cardium edule, Mytilus edulis, Nassarius reticulatus, Littorina littorea and Dentalium. Additionally there is a fresh water bivalve Corbicula fluminalis in considerable abundance. Although known from Pleistocene deposits elsewhere in E. England it is now extinct in Britain but survives in parts of the Mediterranean lands and the Near East. The exact relationship of these gravels to the tills is unsettled. Hessle till probably overlies the gravels and armoured mud balls, apparently of Purple till, have been recorded in the gravels, which, it has been suggested, may rest on Drab till. Whether the deposit is more or less in situ, erratic, or a result of sorting in morainic or esker conditions is also disputable.

Perhaps the most important stratigraphical evidence is an observation made in relation to the Sewerby cliff when obscuring materials had been removed at some distance south of the 'buried cliff'. It is reported that the chalky beach deposit extends over the surface of the Basement till. This, with the 'Moss silts' of Dimlington, demonstrates that the Basement and Drab tills belong to separate glaciations. If this is so the Sewerby fauna belongs to the interglacial between them. An alternative hypothesis is that the Basement clay could belong to an even earlier glaciation. This is feasible if one considers how present day erosive processes could continue to remove material as far back as the 'buried cliff' and still, perhaps, leave some of the tills on the sea floor. Critical evidence is apparently lacking. The dating of the Sewerby fauna could be either that of the Hoxnian or Ipswichian interglacials. Hippopotamus and Didermocerus hemitoechus are more indicative of the latter. Following the interglacial conditions responsible for the cliff and beach the sea-level would fall as ice accumulated to the north. Exposure of the sea bed would provide conditions in which the blown sand could accumulate and increasing cold would form the chalk rubble by solifluxion. The fresh water pools and associated 'Moss silts' would form at about the same time, prior to the advance of the ice-sheet. A radio-carbon dating of the moss gives a time, about 18,000 B.P. (Before Present), corresponding with the maximum of the last glacial.

This leads to the problem of the relationships of the Drab, Purple and Hessle tills. The dating of the underlying 'Moss silts', the widespread presence of Mammuthus and the fresh surface topography place these tills in the last glaciation. The absence of Drab till around Withernsea may be accounted for by postulating its continuity in a depression below present sea-level which may be associated with an earlier Humber but the apparent absence of the two upper tills to the north of Hornsea is not easy to explain. The evidence already presented has excluded the hypothesis that each of the four tills represents a separate glaciation and leaves the difficulty of explaining how the superimposed sequence of Drab, Purple and Hessle tills, as well as their distributional limitations, could be produced as the result of ice-sheet activity within one glacial period. It also seems curious that whereas the Basement till contains erratic masses in the form of 'Bridlington Crag', no such parallel features have been recorded in the upper tills. The fauna of the Burstwick-Keyingham gravels is presumably referable to the last interglacial and early stages of the last glacial. From their position and the presence of Corbicula an association with an earlier Humber may be suspected although other explanations cannot be ruled out.

Two hypotheses can be formulated to account for the existence of the three super-imposed upper tills. First that the ice-sheet front fluctuated, advancing and retreating, so that each till represents a separate advance and the irregularities in their distribution are accounted for by massive lobes developing in the areas concerned. The extensive deposit of bedded silts at the top of the Drab till at Dimlington and the ravines in the Drab till, now filled by Purple till, may have been formed by melt waters of the first retreat; and sandy and gravelly bands between Purple and Hessle tills by melt waters of the second retreat. Gravel deposits such as that at Cottingham and others at the top of the cliffs in various places along the coast may relate to the final retreat. On the other hand disturbances at the junctions between the layers of till or other viable evidence has not so far been reported. The alternative hypothesis is that the ice-sheet was a complex one. Ice approaching from Scandinavia would have other streams from Scotland and, via Teesmouth, from the Lake District fed on to it. On melting, therefore, this complex sheet would produce the more or less distinct layers of till whose horizontal distribution could still be accounted for by lobing of the different layers. Drab silts, ravining, other beds of sand and gravel in the cliff exposures would be formed by the action of water within the melting mass of ice. Even on this hypothesis it is difficult to explain the clarity of distinction between the tills and also the uniformity of the Basement till unless it is only the equivalent of the Scandinavian sheet, the upper portions from British sources being eroded, assuming that both glaciations must have shown corresponding patterns of ice-sheet development. Until such times as more satisfactory criteria can be produced the choice between the two hypotheses should be left open. One depends on the occurrence of advances or 'stadia' and retreats or 'interstadia', for which evidence has been produced in Europe; the other, invoking a multi-layered ice-sheet, may receive further support by a better understanding of the erratic content of the tills.

The final retreat of the ice took place some eleven thousand years ago and sea-level has gradually returned to its present state, though not at a uniform rate. Of the Post- Glacial deposits one type is the 'submerged forest' such as can sometimes be seen on the foreshore at Easington and discovered in dock excavations and elsewhere adjacent to the rivers Humber and Hull. At Easington and along the Humber there is a covering layer containing shells of Scrobicularia, Cardium, etc. recording the rise of sea level. Inside the estuary these shell beds are covered by alluvium. Lake deposits formed in ancient meres, now drained by subsequent erosion, still persist on the coast at places such as Barmston, Hornsea, Sand-le-Mere and Holmpton. Also of interest are thin, white, marly bands, sometimes with fresh-water shells, and black peaty layers which occur in the cliffs about three to five feet beneath the present land surface. These have appeared for short periods between Cowden and Rolston, near Atwick and also around Dimlington and Holmpton. They may be truly Post-Glacial but the possibility that some at least may be as early as the Allerod interstadial, a short warm period at the end of the last glaciation, deserves to be investigated. A summary of one suggested interpretation is given in Table 2, not as a final solution but rather as an invitation to the reader to re-explore and re-examine the evidence, to consider the growth and melting of a series of ice-sheets with interglacials between them, in such a way that one can account for the 'High Level Drift', 'Bridlington Crag', Basement till, the Sewerby Beach, the Drab, Purple and Hessle tills and their distribution, and fit into the latter series the fossils of Burstwick and Keyingham. Perhaps only another glaciation, if one should occur, will provide the vital clues. As a guide to further reading several general works are listed. On Holderness itself the papers by Catt and Penny and Boylan refer to earlier works of which those by Bisat, Carruthers and Reid are of particular value.

Selected Bibliography

BOYLAN, P. J. 1967. The Pleistocene Mammalia of the Sewerby-Hessle Buried Cliff, East Yorkshire. Proc. Yorks. Geol. Soc. 36. 115-125.

CATT, J. and PENNY, L. F. 1966. The Pleistocene Deposits of Holderness, East Yorkshire. Proc. Yorks. Geol. Soc. 35. 375-420.

CHARLESWORTH, J. K. 1957. The Quaternary Era. 2 Vols. Arnold. London.

EMBLETON, C. and KING, C. A. M. 1968. Glacial and Periglacial Morphology. Arnold. London.

FLINT, R. F. 1957. Glacial and Pleistocene Geology. Wiley. New York.

WEST, R. G. 1968. Pleistocene Geology and Biology. Longmans. London.

ZEUNER, F. E. 1959. The Pleistocene Period. Hutchinson. London.

Note about the "Hessle Till" (Mike Horne 2012)

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