|Geological Magazine vol 33(12):533-541.
THE SO-CALLED MIDDLE SANDS AND GLACIAL GRAVELS OF EASTERN ENGLAND
by Sir HENRY H. HOWORTH, K.C.I.E., M.P., F.R.S., F.G.S.
|In a previous paper I have discussed the post-Tertiary Clays of Eastern
England (Geol. Mag., October,
1896, p. 449). In that paper I endeavoured to show that these clays,
varying as they do in texture, composition, and contents, mark a varying
geographical distribution and substratum rather than a succession of changes
in time; that, so far as we can tell, they are for the most part on the
same horizon, and interlock with each other, with occasional local overlaps;
while they are united by one common element, namely, the presence of certain
foreign boulders of the same general type in them all.
These clays are closely associated with largely developed beds of sand and gravel, which present similar problems for solution, and to some hitherto neglected features of which I should like to call attention. Before turning to these sands, etc., I would, however, add one or two additional facts and quotations in reference to the clays in support of my former conclusion. In Norfolk an attempt has been made to separate the so-called glacial clays into a Lower Clay, consisting of a brown stony loam, and an Upper or Chalky Clay, overlain by sands and gravels; but the sections from which this attempted division has been deduced are very uncertain and doubtful in their testimony, and the best authority known to me on the surface beds of East Anglia, Mr. Horace Woodward, says of them: "Most of these sections show in the same pit the sand tapering away, and then the two Boulder Clays come together, and their separation is not a happy task." Again, he says that in many places the Lower and Upper Boulder-clay are identical in character. He further says that, while in East Norfolk the brown clay maintains its character of a brown stony loam, further west "the lower glacial clays become so like the Chalky Boulder-clay that, from the evidence of pit-sections, they cannot he separated one from the other." (Woodward's Geology, p. 5O7, and "Geology of Country round Fakenham, etc.," p 19.) This geographical distribution of the two clays is at once explained when we map out the beds underlying the Drift in Norfolk, and find that in tho eastern part of the county the Chalk is still covered and protected by Crag beds, and was not, therefore, accessible when the Drift was formed, while in West Norfolk the Crag is denuded, as are the other Tertiary beds, and the Chalk itself is exposed. This accounts for the chalky debris in the one clay and its absence in the other. Carvell Williams, in describing the surface beds of Lincolnshire", says: "Near Weston, three miles west of Louth, are good exposures of Hessle Clay banked against the Chalky Boulder-clay"; and he adds the pertinent question- "Does not the brown clay pass into the chalky clay?" Again, he describes at Bricket Wood, in Hertfordshire, a clay as precisely intermediate between the Hessle Clay and the great Chalky Boulder-clay, and adds, "It is clearly both." Again, Jukes-Browne wrote a well-known memoir proving the connection of the Lincolnshire clays with the Hessle clays of Yorkshire (Q.J.G.S. 1879, p. 397).
Let us now pass on. With the post-Tertiary clays, as I have said, are associated large beds of sand sometimes having a gravelly texture, and containing seams of gravel and of laminated brick-earth. These sands agree with the clays in containing the same kind of erratics, and are treated by the orthodox geologists, who champion an Ice Age, as glacial deposits.
As is well known, efforts were made long ago by Binney and Hull, working on different lines and coming to different conclusions, to arrange the so-called glacial beds of Lancashire into three series. Binney divided them into two sandy beds separated by a clay; while Hull, whose division has been more popular, into two clays separated by sands and sandy gravels.
To these sands and sandy gravels of Hull's arrangement was given the name of Middle Sands, because they were supposed to come between the two clays. This tripartite division has caused much heartburning among geologists, who have found it impossible to apply it to the great mass of the beds found outside of Lancashire, or even within that county, and especially has the difficulty been felt in Eastern England, where no sophistication of the evidence enables us to apply such a division or any other yet suggested, and no one has been more emphatic in pointing this out than Mr. Horace Woodward. Speaking of the quadripartite division of Messrs. Wood and Harmer, he says (in reference to the area around Fakenham): "I have been at a loss to find the persistence of any of the above four divisions." The beds have "frequent and often very abrupt changes in lithological characters," etc., etc.
Every geologist known to me of any repute, and working in Eastern England, now repudiates the notion that it is possible to apply any of the plausible divisions which have been suggested to the surface beds of Eastern England; while most of them would agree with Professor Judd in his remarks on Leicestershire, Rutland, etc., that the sands and gravels pass horizontally into boulder-clay, and reject any classification of the beds based upon the alternation of clay with sand. The fact is, not only do the clays and sands run into each other and interlock, but the clays frequently contain pockets and lenticular masses of sand, in many cases of laminated sands with shells, while the sands contain similar patches of boulder-clay, showing they were contemporary or virtually so. Although the tripartite division has not been adopted, the term Middle Sands still figures largely in the literature of these deposits, and occupies a notable place in the index to the Quarterly Journal of the Geological Society.
The geologists of the Survey now generally separate the so-called glacial beds of Eastern England into two series, contrasted sharply by their matrix and texture, namely, the boulder-clays and the sands, etc. While the clays are treated as the remnant of some entirely hypothetical moraine profonde, the sands, which are often stratified and current-bedded, and which cannot therefore be attributed to this fantastic product of Cloudland, are assigned to the action of water. By some this water is supposed to have flowed from the glaciers or ice-sheets in the form of subglacial streams, and by others, who still maintain a tripartite or multiple division, to mark Interglacial climates.
First, a word or two on a critical difficulty for the Glacialists, suggested by the existence of sands and clays in separate and intercalated layers. Every true glacier moraine known to me consists of a perfectly heterogeneous mass of clay, sand, and stones, or of sand and stones mixed in the greatest confusion and quite unsorted. A glacier, or any great mass of solid ice, is incapable, by any known process, of sifting and separating the ingredients in its moraines into sands and clays. Whatever virtues we attribute to ground moraines, we cannot well suppose that the glacier could separate them into the two great constituents of the so-called glacial beds. If the sands and the clays were once mixed in a common mass of so-called "glacier muck," they must have been sifted by something, and that something is shown by the laminae and current-bedding of the sands to have been water and not ice. Water is, in fact, invoked to account for the sands by the ultra-Glacialists, but, if water arranged and deposited the sands, whence did it derive them ? If it washed them out of the hetorogeneous "muck" which formed the moraine, then the clays, no less than the sands, must have been in suspension in the water, and been deposited by it, and if deposited slowly they ought to show, which they do not, lines of continuous stratification. If they came from some other source than this, whence could they have come when the country was, according to hypothesis, either blanketed by ice or covered with the moraine stuff of the glaciers or ice-sheets. The dilemma seems complete. I have put it before, in my "Glacial Nightmare." Of course, I have received no answer. The creed of the Glacialists could not live an hour if its advocates did not persistently hide their heads in the sand, like ostriches, to avoid the most commonplace and every-day evidence. But let that pass.
To a large number of geologists, these so-called Middle or Glacial Sands of Eastern England still index a supposed Interglacial, mild period. It was, in fact, upon the evidence of these very sands that Searles Wood first based his postulate of mild periods in Glacial times. It was supposed to be evidenced by the presence of marille shells in these sands, which could not have lived when the North Sea was choked with its portentous ice burden; and Searles Wood's conclusion is still quoted in some quarters. But the whole induction was really based on a complete mistake of observation. The shells contained in these sands did not live contemporaneously with the deposit of the sands at all. My friend Mr. Horace B. Woodward has shown very conclusively that all the shells and fragments of shells found in the so-called Middle Sands of East Anglia are derivative, and all of those which were formerly supposed to especially distinguish a mild, Interglacial age are really Crag shells, and derived from rearranged Crag beds. This view is now shared by Mr. Clement Reid, who formerly opposed it.
I would carry Mr. Horace Woodward's induction much further. It seems to me that, so far as we have evidence, it extends to making, not only the East Auglian, but all. the shelly deposits of Eastern England, which have been treated as original deposits of the Glacial Age, derivative.
I cannot see how it is possible to separate the isolated shelly beds at March, in Cambridgesbire, from the shell beds of East Anglia, with which they agree so much in texture and contents; while, if we turn to the Yorkshire beds the evidence of their derivative and pre-Glacial character is very marked. These shells occur in the so-called Basement Clay at Bridlington, very often with their valves united, in "transported masses of olive-grey sand and clay." Other similar shells occur at Dimlington in pockets of transported sand which still preserve their lamination, as was observed long ago by Sir Charles Lyell and Professor Hughes, and broken shells also occur there in the clay. Mr. Clement Reid and Mr. Lamplugh have shown that these shells occur, not in situ, but as transported boulders.
The beds in question were formerly boldly called Crag, a name which ought never to have been dropped, for, so far as can be judged, they arc the Yorkshire representatives of the Upper Crag beds in Norfolk, in which, as is well known, Arctic shells occur. It is noteworthy that the beds at Bridlington contain vertebrate remains from the Crag, Eocene, and older beds (Woodward's Geology, p. 499).
It would also seem that the shell beds at Kelsey Hill, near Hull, which are overlain by Boulder-clay at Speeton, where they occur below the Lower Purple Clay, and at Aby, near Claythorpe, in Lincolnshire, are also of late Crag age. I find that after I had written this Mr. Carvell Williams had suggested the same conclusion; and if it be sustained it enables us to solve a considerable difficulty, namely, how to account for the Norwich Crag having been such a local deposit as it has been hitherto deemed to be. It enables us to connect the East Anglian Crag, as Mr. Carvell Williams has done, with the fragments of Crag beds which have occurred on the coast of Scotland in Aberdeenshire and Nairnshire. We must remember that as we get further north we must expect the shells during the period of the Norwich Crag, as in our own time, to show a more and more Arctic facies. I am not sure, in fact, whether all the drift shells on the British coasts which have been treated as glacial are not derivative, and ought not really to be classed as equivalents of the later Crag shells of Norfolk.
With the disappearance of these shells from the category of true glacial debris, and with the proof that they are derivative, disappears the postulate of an Interglacial climate in so far as it has been based on the shelly sands of Eastern England. It also opens the way for an explanation of these sands very different to that usually adopted.
As I have said before, the opinion is now pretty general that all the clayey matrix of the so-called glacial clays of Eastern England is a derivative product, and that it is not, in fact, a clay ground down from argillaceous rocks de novo by whatever distributed and arranged the so-called glacial beds, but that it was ready-made clay when that instrument began its work. It was taken up ready-made from the beds of clay exposed to its influence-in some places the Kimeridge and Oxford Clays, in others probably from London Clay and the clays of the Plastic Series, and in others, from the so-called Chillesford Clays of the Crag deposits.
Everyone who has written in any detail on the subject, seems to allow that the clay which forms the magma or body of the Boulder-clays was derived from pre-existing beds of clay. This conclusion is, in my view, equally true of the so-called sands and sandy gravels. The sands associated with the Boulder-clays of Eastern England are, so far as I know, all derivative also, and were ready-made as sands when the instrument which laid down the so-called glacial beds began to operate. For the most part they are rearranged Crag sands. In part, also, they are probably rearranged sands of the Bagshot and Reading Series; these recent beds having, doubtless, before the denudation of the Fens occupied a much larger area in Eastern England than they do now.
In a very great number of cases where they have been mapped as glacial sands by the Geological Surveyors, I believe it has been through a mistaken notion that Crag sands or Bagshot sands must necessarily contain Crag or Bagshot shells, whereas a very large portion of those sands is barren, and they only become fossiliferous in places. In the Memoirs of the Survey for East Anglia, there are continual laments about the difficulty of separating the so-called Middle Sands or glacial sands from the sand beds of the Norwich Crag. Mr. H. B. Woodward, for instance, says in his memoir on the country round Norwich, in many places there is considerable difficulty in drawing a definite line between the glacial sands and the Norwich Crag where they do not contain foreign stones (op. cit., p. 104). The explanation of the difficulty seems simple enough. There is no difference, except of arrangement, between these sands. The same sands, when they occur in horizontal or undisturbed beds, are rightly treated as Tertiary sands; when they have become contorted and dislocated, or mixed with foreign stones, they are classed as glacial sands, the fact being that they are then merely Tertiary sands remaniés. The so-called contorted drift is probably nothing more than a series of alternating Crag sands and laminated clays which have been twisted and contorted and subjected to violent alteration, and in some cases mixed with some erratic boulders. This mixing and tossing about constitute the sole testimony they offer to their not being true and normal beds of Crag, etc. These so-called Middle Sands or glacial sands in Eastern England have their equivalents on the other side of the North Sea, where they are developed on a great scale, and may be studied in a much more effective and simple way, since they are not associated there with the clays which form such a prominent feature of our own surface beds. In Holland, from Brabant to the Helder, the surface beds which are classed as glacial, lie immediately on Crag beds, which are there developed on a great scale, while there are no beds of Secondary clay or chalk exposed which could supply the ingredients formaking boulder-clays likeour Chalky Clay. etc. These so-called glacial beds in Holland, therefore, consist merely of sands and pebbly gravels corresponding to the Middle Sands which we have been discussing, and consist there, as they do here, of rearranged Crag beds, with a certain mixture of erratic boulders, and nothing more. The matrix of the beds is of home origin, and simply testifies to the Crag sands and gravels having been taken up by some mighty engine, which has rearranged and tossed them about, just as our Secondary and Tertiary clays and sands have been taken up and similarly rearranged. Nor is there a tittle of evidence in these Dutch beds, other than the supposed ice-borne character of the erratics contained in them, to suggest ice-portage or an Ice Age.
To return to England-what the instrument was which tossed the sands and gravels about, formed the contorted drift, and generally rearranged them in this fashion, I hope to discuss on another occasion. At present it will suffice to draw the same negative conclusion from the sands that we have already drawn in regard to the clays.
In my former paper I examined every feature of these clays in succession, and endeavoured to show that in no single one do these clays support the notion that they were formed or distributed by joe; hut, on the contrary, when critically examined, their texture, contents, mode of occurrence, etc., are absolutely inconsistent with ice in any form having had to do with them.
If this be so with the clays, a fortiori is it so with the so-called Middle Sands. These sands are stratified, laminated, and false-bedded; they present all the features of subaqueous deposition and arrangement, and it is universally concluded that they were, in fact deposited by water. The champions of the Ice Age save their consistency, as I have said, by postulating that the sands were either distributed and laid down by subglacial streams or during an Interglacial, temperate period. I have already discussed the latter issue. In regard to the former let me add one further argument. These sands and sandy gravels are distributed in a most erratic fashion-sometimes, but rarely, in the valleys, sometimes capping the hills, sometimes on the slopes. How subglacial streams could run about the country, irrespective of its drainage and surface contour, uphill and downhill, and deposit these beds as we find them, passes all belief. The fact is, that directly the Glacialist has secured his ice-sheet, and covered the land with it, he considers that he is entitled topostulate any kind of mechanicalabsurdity as having occurred under its shelter-to believe in the moving about under a portentous weight of hundreds of feet thick of slippery clay, and sliding pebbles, and disintegrated sands, as of ice, ground moraine; the running about of water up and down the country, contrary to and in spite of gravity. These are samples of what is commonly supposed to have occurred in the far-off days when ice was everywhere. In fact, with the intervention of these entirely imaginary ice-sheets we are naturally transported to an entirely imaginary world, and entirely imaginary operations of nature.
While the ultra-Glacialists admit the deposition of the so-called Middle Sands by water, there is one feature developed locally in them which many of the prophets of ice attribute directly to ice action in the form of floating bergs, or of the melting of subterranean ice, namely, the contortions which occur in the so-called contorted drift, and the curves and twists of the laminar beds of sand, etc. Upon these I must add a few words. I have spent many scores of days on the coasts and in the sand and chalk pits of East Anglia, and have drawn a good many sections there. Many a time have 1 wondered how it was possible for any human being who realizes what a grounded berg is like, and the kind of mechanical work it can do, to suppose that it could possibly fashion the long-continuous, beautifully modelled curves into which the sandy laminae have been arranged, many of them extending for hundreds of yards without any breach in the continuity of their graceful lines, in many cases twisted into various serpentiform curves, which are often reversed. How a solid, heavy mass of ice, pounding down upon soft debris, marked by delicate lines and laminae, or pushing over it, could avoid pounding it into what the Americans call "muck," or could in any way arrange the curved laminae of the contorted drift as we see it in the cliffs of Norfolk, is a stupendous mystery to myself and perhaps to many other people. How it would be possible, again, to either create or maintain such curves and lines by the collapse of portions of soft beds in consequence of the local melting of buried layers of ice, as some others have argued, is equally confusing. The unsophisticated student who has drunk at these orthodox geological wells should suspend his judgment on these conclusions until he has actually seen the gigantic swirls and figures of curves, which are so frequent in the Cromer cliffs, or mapped out carefully a series of the layers all arranged in concentric curves round some lenticular or other nucleus, of which examples occur at every few yards in the cliffs. The fact is, such reasoning as I am criticizing is the despairing death-song of Uniformity as understood by some of Lyell's scholars.
Not less impossible to attribute to ice-action, as we have shown in previous papers, is the presence in some of these contorted beds of great masses, not only of solid chalk, but of loose and soft materials, of pockets of sand or lumps of shale, which have been taken up and redeposited with their fine laminae undisturbed, and the shells in them unbroken and transferred as boulders into the beds in question. That grounded bergs or coast-ice should have performed this kind of work, is as credible to some of us as that Nasmyth's hammer should have come down on a raspberry sandwich and left the indigestible layers intact. I claim to have shown that in no single respect do the so-called Middle Sands, so far as I know them, either testify to the action of ice in any form or to the existence of glacial conditions when they were deposited, nor to the existence of Interglacial periods: conclusions which I share in, as far as East Anglia is concerned, with one of the ablest and most experienced prophets of Neo-Glacialism, Mr. Carvell Lewis.
Having dealt with the post-Tertiary clays and sands, we still have to consider another set of beds, associated with them in Eastern England and marked, like them, by the presence of foreign stones. These are the beds of gravel and shingle (for the most part clean-washed), and consisting, with the exception of the comparatively small proportion of erratics they contain, of smooth flint and quartzite pebbles of a lenticular or flat, oval shape, and occurring in many cases as caps to the hills or on their flanks. Many of these were formerly treated as gravels formed in subglacial streams or by interglacial rivers.
The opinion has been gradually gaining ground lately, however, owing to the admirable work of Prestwich, Searles Wood, Monckton, and others, that the pebbles in these shingle and gravel beds were formed and smoothed as we find them long before the so-called Glacial Age. With the contour of the country as we know it there are no rivers in Eastern England which either make or can make gravel or shingle, nor do we see whence the original stones could have been derived under present conditions for fashioning the pebbles. These pebbles are precisely like in form and in character to the pebbles occurring in the Bagshot and Reading beds. Where they occur in East Anglia, etc., in regular beds and undisturbed layers, as they do at Southwold and in other places, it seems to me that they actually represent Tertiary horizons. Where they occur mixed with foreign stones and disturbed, they form another instance to be added to those already quoted or Tertiary beds which have been remanié and redistributed by the same force and at the same time as the various Boulder-clays were distributed. Let us now sum up some conclusions-
1. A general and most important result from these arguments and facts, if they are sound, is, that whatever it was that mixed and distributed the soft surface beds of Eastern England, the Boulder-clays, so-called Middle Sands, and the gravels, it had no part in manufacturing the ingredients out of which those beds were fashioned. These ingredients, in so far as they were local, were already fashioned and ready to its hands. The clays were already there in the form of clay; the chalky, Oolitic, and Liassic rubble was there in the form of rubble; the polished flint and quartzite pebbles were there in the form and shape we now find them; and the shells were also there, having lived in the Crag seas.
2. What the instrument alone did which formed these beds as we them, was to bring with it a certain number of foreign stones and to mix them with the ingredients already on the ground and then to distribute the product as we find it distributed.
3. There is no evidence in these beds to justify our postulating long process and a prolonged period as necessary for this work, such as the fashionable school of geologists postulate, who profess to account, not only for this mixture and distribution, but for the manufacture of the ingredients, by invoking the long continued action of ice during an Ice Age. On the contrary, there is every ground for believing the process to have been rapid, and, if not sudden, to have been continuous and not intermittent.
4. There is no ground, so far as these beds or their contents are concerned,
for invoking the intervention of ice in any form in their mixture and distribution,
but every feature which marks them is at issue with their having been the
handiwork of ice. The term glacial, therefore, applied to the clays, sands,
and gravels in question, is inapplicable. It is quite time that the authors
of this literature should put on their armour and sharpen their weapons,
and instead of repeating the obiter dicta of their wildest prophets, should
condescend to examine the facts and arguments which have been quoted against
them and to reply to their critics.