KELSEY HILL AND OTHER DRIFT PROBLEMS.
(Presidential Address: March 20th, 1924.)
allow me a retrospective glance, in addressing you on an occasion over a
quarter of a century ago (just twenty-six years in fact, but the
century-fraction strikes the time more impressively), I
used the opportunity to enumerate certain gaps in our knowledge of East
Yorkshire geology [
Some open questions in East Yorkshire Geology
] . My address was printed in your Transactions, and by
reference to it we can measure the substantial progress that has been made
towards filling the gaps, a task in which the
There were questions as to
Some advance has likewise been made on almost all the other problems I mentioned, and though some are still unsolved, their solution has been, at least, approached.
Two of these I propose to take as the subject of my present Address ; not with a solution to offer, but in order to analyse the difficulties and to stimulate a further attack upon them. These are both directly concerned with Drifts of the Humber Gap. They are (I) The shelly gravels containing Corbicula fluminalis, and (2) The Kirmington Estuarine Deposit. On both problems I shall offer opinions, but with the consciousness that they are in neither case decisive, since the evidence at present available falls short of affording certainty, thoug'h sufficient to justify an opinion.
(i) THE KELSEY GRAVELS.
Shelly Gravels have been a problem ever since 1828, when John Phillips first
called attention to them. Why do they become suddenly so richly shelly at
Kelsey Hill, and what is Corbicula--a fresh-water shell--doing in
that galley where all the other shells are marine? The Kelsey gravels form a
link in the chain of gravelly mounds which is traceable from the summit of
Flamborough Head, across Holderness, to the Humber, and is seen again south
of it in
As to the identity of the shell with the living form, I have sought the opinion of my friend Mr. A. S. Kennard, our leading authority for Pleistocene and Recent Fresh-water Shells, who kindly permits me to quote, as follows, from his reply :--" Now, the Kelsev shells are Corbicula fluminalis (Mull.) ; at least they are the same as the Pleistocene shells so-called from many English deposits, and I cannot find any real difference between them and the Euphrates and Nile shells. And they are derivatives. They were fossil before they got in the Kelsey gravel. The worn condition of some of the umbos is clear proof to me. By the way, some are marked with dendrites: are the other Kelsey shells marked in a similar way ? That is, I think, a point to be settled."
It was long ago. recognised by Gwyn-Jeffreys and Prestwich (Q.J.G.S.,
pp. 448-51) that the shells at Kelsey Hill .ere not in their original
habitat and had been swept together from various depths and surroundings.
Nevertheless it was taken for granted that the gravels were marine, a view
that is still to some extent current. But the continued study of the shelly
drifts of Britain has led gradually to the recognition that where ice-sheets
of the Glacial Period have been forced inland from the old sea-basins they
have almost every-where brought in marine shells or shell-fragments along with
their other detritus, just as modern ice-tongues have been observed to do
Granting this mode of formation for the gravels, we have still to seek an
explanation for the anomalous admixture of the Corbiculae.
they should exhibit themselves around the
But if Corbicula were not a
It is true that, against this idea of an easterly source, there is a particular objection in the absence (so far as is known) of Corbicula from all the boulder-clays and stratified drifts of the coast-sections to the eastward in Holderness, although most of the marine species associated with it at Kelsey may be found, therein.
To meet this objection, it can be argued that the glacial river may have swept the shells together from parts of the sheet which lay farther eastward than the present coastline: or, alternatively, that the upper layers of the ice may have carried material quite different from that in the lower layers---as I have myself seen in a flat-lying glacier in Spitsbergen. The latter possibility is indeed illustrated in the Holderness cliff-sections of boulder clay, where bands of strikingly different composition, rudely stratified and sometimes contorted together, often occur within the limits of a single closely-welded bed. From observations in other localities also, I think that the bringing together of different constituents into juxta-position in this way has been common whereever an advancing ice-flow fins impinged upon a rising slope, and is to be explained by the tendency of this condition to cause a blockade of the lower part of the ice and an over-riding or over-thrusting of it by the oncoming parts of the mass. The occurrence of broad fiat belts of thick boulder-clay, as in Holderness, is generally observable w'ith these circumstances ; and such belts formed near the margin of the ice-sheet might be described as "expanded moraines." The Kelsey gravels lie above a belt of this kind, and therefore are likely to contain the material brought in by the upper layers of the ice.
However, whether we look east, west, or underground, for the origin of the
are difficulties. And so the problem stands! What is especially to be
desired is that some fresh-water deposit should be found in the
While on the subject of the South Holderness drifts, I may be allowed to add a word or two on new information obtained not long ago from Government borings near Spurn. I was able to examine samples of the material from one of these at Kilnsea, which penetrated deeply into the Chalk. Often when at Dimlington. I have wished that we could get to know something of what lay between the shelly Basement Clay seen at low water there and the deeply-buried Chalk, an unknown space with room in it for many possibilities. Forest Bed or Crags, perhaps? The boring gave the answer and dispelled the hope for such novelties. From the record and the specimens (of which I published a short account in the "Summary of Progress," Geol. Surv. for 1918, pp. 63-4), it is clear that drifts similar to those seen in the Holderness cliffs extend right down to the Chalk here. The boring started at 25 ft. above O.D. ; and down to 127 ft. it passed almost entirely through boulder clays, mainly of the ordinary dark purple type, and not, in any of the submitted samples, notably shelly. I have long suspected that the very shelly portions of the so-called " Basement Clay," seen on the shore at Dimlington, Bridlington, and in rarer exposures in Filey Bay, are really only local lenticles, occurring in the thick mass of the lower boulder clays, like the smaller lenticle I found many years ago in the cliff at South Sea Landing; and this we may now safely assume to be the case. The shelly character is confined to bands or streaks, and does not pervade the whole thickness of the lower boulder- clays. Also it goes without further saying that nothing resembling the Corbicula-gravels of Kelsey Hill was encountered in the specimens from the boring.
127 ft. the boring passed through a few feet of stratified silty clay and
sand and then into tough "chalk-wash," this part of the section being
apparently quite similar to that seen at the bottom of the drifts in the
cliff section at the mouth of Danes' Dyke, and at Flamborough North Sea
Landing. The thickness of the " chalk-wash " was not precisely determinable,
(2) THE KIRMINGTON DEPOSIT.
let us turn to the other perplexing problem of the
bed was first noticed by Wood and
patches of red weathered boulder-clay (now no longer seen) and several feet
of coarse shingly gravel (still visible) overlie the estuarine bed, and
betoken Glacial conditions in the locality alter the deposition of the warp
; while the boulder-clays and stratified drifts proved in the borings afford
clear proof of Glacial conditions here before the estuarine episode. The
shells of the warp, few in number and in species, are clearly in their
original .surroundings, the bivalves generally with valves united; and all
are such as still live together in estuaries throughout the North Temperate
and Boreal regions of
particular interest of the section lies in the fact that here we have
convincing evidence for a marine intercalation between deposits of Glacial
origin; and it is the only place known to me in
Moreover, the estuarine material reaches a height of close upon 100ft. above O.D.; and as it must have been laid down in very shallow water, probably between tide- marks, it may be taken to denote the exact measure of the submergence during its accumulation.
But think what this implies! A submergence of 100 ft. would put all Holderness under water; and all the country east of the Wolds in Lincolnshire; all the Fen country farther south; all the Vale of Ancholme; most of the Vale of York; and great spreads in the valley of the Trent right up to Newark; not to speak of the wide regions, both northward and southward, more remote from Kirmington. Yet in all this area there has been nowhere found anything comparable to this Kirmington deposit; that is to say, no deposit intercalated with the drifts above present sea level containing an indubitably indigenous marine fauna. On the contrary, everywhere else on these low grounds we seem to have clear indication of continuous sub-aerial erosion during and since the closing stages of the Glacial period. Why should the Kirmington evidence be so exceptional? That is the puzzle: and the solution of it is yet to seek.
It is true that for evidence of the character and contents of a deposit of this kind we have to depend upon an artificial opening, and if it had not been for the Kirmington brickyard, we should have remained ignorant of this instance; so that other occurrences may remain undisclosed. But in these well-populated lowlands the presence of a useful stoneless brick-earth is pretty certain to have attracted practical attention in the past, when the making of bricks and tiles was distributed almost entirely in small local yards. Also, the whole of the ground has been systematically examined by the officers of the Geological Survey, which again reduces the chance of undiscovered occurrences.
I am satisfied, after repeated examination, that we cannot, at Kirmington, invoke the agency of transportation by ice to explain the facts. The conditions are quite different from those displayed by the mixed shreds of sea-bottom among the boulder-clay at Bridlington, Dimlington and other places on the coast, where we are driven, by clear evidence, to this explanation. The present sequence at Kirmington is a natural one. As I interpret it, we have, in the Glacial sand and gravel which forms the floor of the brickyard, the thaw-water outwash from the retreating ice which had previously laid down the deep lying boulder-clays proved in the borings. What I think must be a continuation of the same sand and gravel was formerly exposed at about the same level in a small pit in the hollow near Croxton, three-quarters of a mile N.N.E. of Kirmington, where it has yielded the usual worn and fragmentary marine shells of the Holderness gravels, including, as previously mentioned, three specimens of Corbicula fluminalis. Reid considered this sand and gravel to be the off-shore representative of the Kirmington warp, and spoke of the two together as the deposits of the "Croxton and Kirmington fjord." But both the physiographical and the new stratigraphical evidence tell against this correlation, and I think we must regard the estuarine warp as indicative of a different set of conditions marking a definitely later stage. The presence of peat and of loam with fresh- water shells, above the sand and gravel but below the estuarine deposit, denotes that the tract was above sea level for a time, anterior to the estuarine phase. It seems most probable therefore that the sandy out-wash gravels were themselves spread upon a land surface, or, at least, on an area which could be converted into land by the very moderate thickness of the gravelly deposit. As we have no actual indication of the sea-level at this time, we cannot measure the maximum amount of the later sub- mergence; but it must at least have exceeded 20 ft., to allow the accumulation of the thickness of warp seen at Kirmington. If the laminated clays exposed in a brick-yard at Great Limber, about three miles S.E. of Kirmington, belong to the same episode, as Reid suggests, the bounds of the submergence would be raised by another 20 ft., as the deposits there reach to at least 120 ft. above O.D. But no shells or other fossils have been detected at Limber; and the laminated clays differ also in other respects from the Kirmington warps, and appear to be nearer akin to the laminated drift formerly so conspicuous in the cliff at Hilderthorpe, south of Bridlington, which we interpret as the product of a local ice-dammed lake.
is, however, not unlikely that, granting the unfossiliferous laminated clays
of this type to be thaw-water sediments deposited in pools bordering the
ice-sheet, yet the general level of these pools may have been governed by
the sea-level of the period; and that there may have been connexions, more
or less open, between there and the sea. Certainly, the levels round about
100 ft. above present O.D. seem to have had some controlling influence upon
a considerable portion of the stratified lowland drifts of Yorkshire and
But let us leave the question of levels for the moment, in order to consider the topmost beds of the Kirmington section. These betoken strangely different conditions from those of the estuarine warp stage. The coarse battered shingle of flints with a few foreign stones, 8 or 10 ft. thick in places, directly overlying the warp wherever the section approaches the crest of the rising ground, was described by Reid as " beach shingle," thereby implying wave-action. But the Chalk valley is long and barely half a mile wide, with gentle slopes on both sides; and, as we know now from the borings, the Kirmington hillock lies about midway in this valley, with no bare Chalk in the immediate vicinity. It is inconceivable that wave-action powerful enough to form a shingle-bank so coarse and thick as this could arise in so narrow an inlet. Moreover, the shingle has none of the distinctive characters of a beach-shingle, but is like the bouldery " cannon-shot" type of Glacial gravel. It has its nearest analogue in the moundy: crescentic mass of bouldery gravel associated with boulder-clay occurring at Wrawby near Brigg, five miles west of Kirmington. This mass of drift is the most conspicuous feature on the low ground of this neighbourhood west of the Wolds, and is just opposite the gap in the Chalk at Melton Ross, which breaks by a low col into the Kirmington valley. The moundy mass, largely consisting of chalk and flint, appears from its shape ant composition to have been the moraine of a tongue of ice which passed westward up the Kirmington hollow and through the gap at Melton, at a late stage of the Glacial period. The relationship of the drift to the gap is well illustrated by the one-inch Geological Survey map (Old Series, Sh. 86).
think that we can reasonably interpret the top "' Shingle " at
Kirmington as part of the same story, and
Now let us consider further the difficulties in which we are involved. The shell-bearing warp, if deposited at its present level, proves a submergence of 100 ft. at some stage between the beginning and the end of the glaciation. But why is the evidence confined to this one spot, and unobtainable elsewhere in the wide extent of adjacent country, both east and west, at or below this level? And from which direction--east or west--did the salt water obtain access to this sheltered valley? I have sometimes speculated on the possibility that the bed, although on its original site, may have been bulged up above its original level, along with the drifts beneath it, by the pressure of the tongue of later ice which re-invaded the valley and brought in the capping drift. This kind of elevatory movement does appear to have taken place at Speeton, where there is evidence that the shelly bed at the base of the drifts has probably been lifted to its present position of some 90 ft. above sea-level by the bulging up-creep of its foundation of Speeton Clay under the pressure of the neighbouring chalk escarpment. But the possibility of any such agency at Kirmington is very remote; and, even if entertained, it really does not help matters. For, supposing the bed to haw been deposited at any lower level, we are faced still more acutely by the difficulties of explaining its absence from the coast- sections and of finding a place for it in the Glacial sequence seen there.
Excluding the great gap of the Humber, it is note-worthy that the gap through the Chalk Wolds at Kirmington, with a present passage at 80--85 ft. above O.D., and a still lower passage if all the drift were removed, is the only other, place in the whole of the Chalk range between the Wash and the Vale of Pickering where the hills are broken to below the 100 ft. contour; and I think that this fact may have something to do with the unique occurrence and preservation of the estuarine bed. Some further evidence bearing on the pre-glacial condition of the Kirmington valley has come to hand since our borings were made in 1903- 4. Borings for water at Brocklesby, 1½ miles E.N.E., and at the Immingham Docks, 6 miles E.N.E., of Kirmington, of which particulars are preserved at the Geological Survey Office, have revealed the presence of a drift-filled trough in the Chalk, which appears to be the down-stream prolongation of the Kirmington hollow.
At Immingham the Chalk-floor is at about
240ft. below O.D.,
and at Brocklesby at about
below O.D., while, as previously stated, we found it approximately at O.D.
do not know that any of the borings actually touched the deepest part of the
valley in their vicinity; but whether they did or not, it is clear that the
down slope of the valley-floor is very sharp, and denotes a stage of
intensive erosion and relatively high elevation before the onset
the Glacial conditions. This bears out the evidence north of the
Later, however, during the glaciation, the low escarpment saddle
between Kirmington and Melton Ross was
Nevertheless, thee absence in the surrounding country of any of the more lasting traces of a coast-line, such as a shore-platform or an old base-level, is remarkable, and appears to indicate that the submergence was of short duration. It is evident, also, that there has been much re-modelling of the surface by subaerial agencies since this period, particularly in the area west of the Wolds; and the retrogression of the Chalk escarpment in this quarter has almost certainly been deep enough to explain the disappearance of any narrow shore-ledge which may have existed on its flank.
I have still avoided the question whether the salt-water invaded the col
from the east or from the west, or from both sides simultaneously ; and, in
truth, I can find better objections against, than reasons for, either an
easterly or a westerly sea. I hope that the Hull geologists will sooner or
later bring some nmv evidence to bear on this aspect of the matter which
will rescue it from the realm of speculation. Bur the best guess I can give
at present --a guess that I first entertained over 30 years
ago and have not
been able to better--it is that
rise of sea level
followed upon the maximum glaciation, when the East
British ice reached its farthest up the easterly slopes of the Yorkshire
Wolds and covered most of the Lincolnshire Wolds and all the great Fenland,
while the Pennine glaciers overspread the Vale of York and the more
southerly part of the Humber basin to at least as far south as Retford and
Gainsborough. By these ice-sheets the sea would be blocked out from the
low-lying areas which would have otherwise been submerged, and the boundary
between land and sea would be as confused as it is now in
the waning of the glaciation and the consequent recession of the ice-border,
the sea would creep in along its margin wherever the land was low enough ;
but would still be confined to the uncovered tracts, irregularly localized
and determined by complex factors, as they are at present in
still hold that the evidence of the coast-sections between the Humber and
the Tees can only be interpreted on the supposition that the basin of the
North Sea, in these latitudes was occupied by an ice-sheet continuously from
the beginning to the end of the production of the Yorkshire boulder-clay
series, and that the marginal recessions were irregular and partial. The
main recession was that which occurred just before the deposition of the
Hessle Clay; and it appears to have been during the later portion of this
interval that the estuarine waters invaded the Kirmington gap. The
is my working hypothesis. I am conscious of the weak places in it, and of
difficulties which arise when we seek to extend it beyond the
[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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