|Geological Magazine 1896:58-66.
THE DESTRUCTION AND SHATTERING OF THE CHALK OF EASTERN ENGLAND.
by Sir HENRY H. HOWORTH, K.C.I.E., M.P., F.R.S., F.G.S.
|A SHORT time ago I read a paper before the Geological Society, of which
an abstract appeared in the Proceedings, in which I discussed some questions
of critical interest in the geology of East Anglia.
I am more than pleased to find that some of the conclusions I pressed, and which I had long ago reached, have been discussed by two such excellent geologists as Professor G. A; Cole and the Rev. E. Hill, whose papers were printed in the December Number of this MAGAZINE (pp.553 and 555).
That the Chalk of Eastern England was originally laid down in horizontal beds no one will, I presume, deny. That since it was so laid down it has been folded and bent into vast curves, no one who has studied either the surface contours or the well-borings will venture to question. That this folding of the Chalk into a series of wolds with intervening valleys must necessarily, unless the Chalk could slip over its lower beds, have been accompanied by enormous fractures and by the breaking up of large portions of it into fragments, is as clear as any mechanical problem can be.
When we turn from this a priori reasoning to the actual facts we can hardly doubt that the Chalk of Yorkshire, of Lincoinshire, and of East Anglia, which now exists in a disconnected and discrete form in these three areas, was once continuous, and that the vast mass of chalk rubble which exists in the chalky clay of the Eastern and Central Counties of England, is the result of the violent disintegration and dislocation of the beds once occupying large areas ow denuded of their chalky covering, and notably of the depression in the Fenland. This dislocation and disintegration I hold to have been coincident with the spread of the chalky clay, and to have occurred, not in the older Tertiary times, but to have been the very last chapter of East Anglian geology.
Let me first partially clothe my heretic self in the garments of some orthodox men. Professor Seeley argues that before the Drift began a Cretaceous barrier dammed out the sea from the Fenland, extending from Hunstanton, in Norfolk, to Wainfleet, in Lincolnshire; and he further argues that before the Drift began this barrier was not broken through (GEOL. MAG., Vol.111, pp. 1-3). Mr. Skertchly agrees in this, and says that before the Glacial age the site of the Fenland basin was very different from its present condition. The Chalk and other Cretaceous and Neocomian rocks stretched from Hunstanton to Lincolnshire, across what is now the mouth of the Wash (Geology of the Fenland, p.217).
While the orthodox geologists are quite willing to allow this considerable denudation in comparatively recent times of the Chalk country of Eastern England, they mostly attribute it to the effects of either marine or fluvial denudation, or to the action of ice, and do not correlate it with the general alteration of the contour of the country by which the North-and-South-Chalk Wolds of Eastern England were formed.
The following sentence in a paper by Mr. Horace Woodward condenses the current view of the Uniformitarians on this point. "Mention," he says, "has previously been made of the connection of the Norfolk Chalk with that of Lincolnshire. In Miocene and Pliocene times, rivers may have commenced to erode their courses in it making outlets to the sea. These actions (to quote Mr. Skertchly) resulted in reducing the barrier to outliers; one between the Witham and the three united rivers (Welland, Nene, and Ouse), the other between that united stream and the Little Ouse. As submergence went on, the sea added its powers to that of the rivers, and finally the Chalk disappeared entirely. The sea was now brought directly in contact with the widespread outcrops of the yielding Kimmeridge and Oxford Clays, and the denudation of the Fenland basin proceeded at a rapid pace." ("The Scenery of Norfolk": Trans. Norfolk Nat. Soc., iii, 445.)
Mr. Skertchly and others merely treat the chalk lumps as the debris of marine denudation.
It seems to me that whatever theory is adopted to account for the chalky clay itself and its distribution, it is impossible to attribute the disintegration of the chalky and oolitic debris which it contains to any such diurnal causes as are above mentioned. This chalky debris is nearly all angular or subangular, and absolutely different in kind to any marine shingle or river gravel in the world; and those who have handled, as I have done, many thousands of the lumps of the chalk (it is utterly wrong to call them boulders), with their angular edges and their contour like broken road-metal, cannot, it seems to me, without absolutely forsaking all inductive methods, see in them the debris of marine or fluviatile denudation.
Not only is the angular form of the pieces of chalk incompatible with a fluviatile origin, but the great masses of shifted chalk and oolite, to which I shall presently refer, are still more so; while as to the sea, not only do these same arguments apply, but we have no trace in the Fen country, or in the valley of Axholme and its borders, of the continued presence of the sea there consistent with slow marine diurnal denudation-no old sea margins or shingle beds, no rounded pebbles, except Tertiary ones, and no marine debris of the kind we should certainly find, while the whole of the deposits are entirely different to those of an advancing or retreating sea.
Other people have in these latter years attributed the breaking up of the Chalk to the action of ice, either to land-ice or icebergs or coast-ice. Mr. Jukes-Browne, Mr. Hill, and others have spoken strongly and well on the subject of land-ice, and shown how impossible it is to credit this stupendous denudation to ice in this form. In addition to what they say, we nowhere find glaciers breaking up their beds in this way, not even in Greenland or Alaska, nor is it credible that they should do so if the mechanics of the problem are for a moment considered.
The Chalk-stones, again, are quite different to ice-stones of all kinds known to me, and the occasional scratches on the pieces of chalk, which is a very soft substance, would be certainly caused by any movement in which one stone rubbed against another.
Again, as to icebergs, it is forgotten that it is only when grounded dynamically that they act in the way suggested. When they are floating they are buoyed up by the water, and their pounding action must be very slight. The intervention of coast-ice has been called in by Mr. Mellard Reade to account for the long chalk masses in the contorted drift at Cromer, but he overlooks the fact that similar shifted masses occur in Rutland and Lincolnshire formed of the local rocks there, where no old sea cliffs can be postulated.
Lastly, the suggestion that rocks might under the influence of alternate frost and thaw break up into such rubble as this, is again completely contrary to all experience of Chalk known to me (except on exposed cliffs, and even here very slightly indeed, as we can see by walking along any of the great escarpments which bound that deposit), nor can I see how the mechanical process could begin or go on in a substance with the structure of chalk. Besides, why should the frost have broken up the chalk in the low Fens and left it intact in the welds, where it would be so much more exposed to its influence. The position is not arguable.
These various facts and arguments seem to we to converge upon one conclusion, namely, that the denudation of the Chalk and other beds in Eastern England was not and could not be the result of diurnal causes. Let us now try and examine the notion that the ruin of the Chalk was the result of the breakage and disintegration of the strata which occurred when the present contour was given to the country.
First, let us turn from the chalky rubble to the well-known gigantic masses of chalk and oolite which occur occasionally in the Eastern Counties, and to which I have referred. These have always been a crux to the advocates of diurnal methods of denudation. Rivers or sea-waves can hardly move about twenty square miles of Chalk en bloc over leagues and leagues of country, and those who believe that land-ice or glaciers could do this, must have some special acquaintance with the inner workings of ice which has not been given to those who have seen it at work in its own special home. To me, who am only a heretic, these great masses now found detached and isolated are not far.transported boulders at all, but are virtually in situ, the remains and relics of the once continuous strata which occupied the areas now largely denuded. If they have been moved, it has been a very short distance and by some tremendous motive force which may have temporarily lifted them and underlaid their edges with chalky clay, but otherwise they are at home where they were originally made and deposited, and are no vagabonds and wanderers. This conclusion I have long held, and it seems to me more consonant with probability than any other. As the matter is of more than usual importance I should like to enlarge a little upon it.
Writing in description of the Geological Survey Map, Sheet 64 (Rutland, etc.), Mr. Judd says : "The transported masses of local rocks are sometimes of enormous size, especially in the northern portion of this area and in that to the south. The attention of geologists was first directed to these great tran8-ported masses by Professor Morris, who found that at the south end of the Stoke tunnel on the Great Northern Railway an enormous mass of the Lincolnshire Oolite limestone lay on undoubted Boulder-clay. During the mapping by Messrs. Holloway, Skertchly, and myself, of the districts which I have indicated, we have found a number of such transported masses, some of them far exceeding in size that described by Professor Morris, and composed both of the inferior Oolite and the Marlstone rock-bed. Their position is indicated upon the Drift map. They always appear to occur in the lower part of the Boulder-clay, and by the denudation of the softer surrounding material often make a distinct boss, rising above the general surface. Stone pits are often opened in them, and they sometimes give off springs at their base. The longest of these transported masses, that capping Beacon-hill in Sheet 70, is more than 200 yards across, and is composed of the Marlatone rock-bed. It is noteworthy that these masses always belong to the rocks which form the highest ground." (Geology of Rutland, etc., p.246.)
When we turn to Professor Morris' paper on one of these famous boulders, it is interesting to see him suggesting that it was not a far-transported boulder, but in situ, or virtually in situ.
Professor Morris, speaking of these beds in Lincolnshire as long ago as 1853, says of the famous Ponton cutting: "The oolites are frequently dislocated, the dislocated portions lying at high angles, and are very irregular. . . . Emerging from the south end of the tunnel [at Great Ponton] . . . . we see the drift on either side of the cutting buoying up an enormous irregular mass of ooiitic rock through which the cutting has passed. This mass of rock is 480 feet long, and at its deepest part 80 feet thick; it is much broken and disturbed, but the parts retain to some extent their relative position, and belong to the lower portion of the oolitic beds of this district . . . . The depth of the underlying drift exposed at the lowest part between the broken rock and the level of the railroad is about seven feet. . . . this great mass of disturbed oolite, which, although so distinctly isolated, retains sufficient uniformity of character to lead us to infer that it has not been far removed from its original site." (Q.J.G.S., vol. lx, pp. 318-320.)
These great masses of shifted rock, of course, occur elsewhere. The typical instances are those in the Norfolk cliffs - that in the Roslyn hole near Ely, the great Morton boulder in West Norfolk, and, more remarkable than all, the great mass of chalk, twenty miles square, recently found by Mr. Cameron on the borders of Huntingdonshire and Bedfordshire. These, and such as these, seem to me to be instances, not of vast transportation, but rather the remains of once continuous strata, and closely allied to the actual outliers found in the county of Cambridge, west of the escarpment of the chalk, and to testify to the once continuous Chalk having been dislocated in situ by some far reaching subterranean force.
Let us now turn to the evidence that the Chalk has been so dislocated and broken in comparatively recent times.
In many places in Norfolk there have been found, as is well known, evidences, not only of chalk quite disturbed and disintegrated, and reduced to a rubbly condition, but also instances of its being curved and tossed up on end. These disturbances, in the view of some of the best observers, like Mr. Horace B. Woodward, Mr. J. E. Taylor, Mr. C. Reid, Mr. Jukes-Browne, etc., belong to the same date, and were caused by the same forces that made the Boulder-clay. As the matter is one of considerable importance to the argument, I propose to quote some of these cases as described in the Survey Memoirs and elsewhere.
In the GEOLOGICAL MAGAZINE for 1865, Mr. J. E. Taylor described a saddle-shaped anticlinal or ridge in the Chalk at Whittingham. The beds, with conspicuous bands of flints, were so bent as to form an acute angle, which was very well defined. The layers of flint were not shattered, nor were the strata broken. At first Mr._Taylor attributed this disturbance in the Chalk to a time before the deposition of the Norwich Crag, but he subsequently (id. Vol vi) attributed the twisting and dragging up of the Chalk to the agent which formed tho Upper or chalky Boulder-clay, a view in which Mr. Horace B. Woodward concurs (id. Dec. II, Vol. VIII, p.93).
In 1866 Mr. Taylor called attention to a similar disturbance in a pit at Swainsthorpe. He tells us that on the left side of the pit the flint bands were nearly perpendicular, being somewhat contorted and leaning towards the right. On the right side the bands were somewhat more perpendicular, but still leaned towards the north. The contorted bands forming an anticlinal arch, the summit of which had been denuded . . . . flint bands were shattered and broken as though by the influence of some sudden force. (GEOL. MAG., Vol. III, p.44.)
A similar disturbance occurs in the Chalk at Trowse, and was first pointed out by Mr. T. 0. Bayfield. In this pit the Chalk, with layers of flints and paramoudras in situ, was inclined at an angle of from 350 to 400 in a south-easterly direction. Mr. Woodward found the bedded chalk pass into sandy and many beds, and itself contained fractured flints with pebbles of flint and quartzite, which were dispersed throughout it. The flint layers gradually assumed a horizontal position in going downward. He adds - "From the fact that beds of the age of the Norwich Crag are disturbed together with the Chalk, it may he concluded that they were forced up in post-Pliocene times; and from the relations borne by the chalky Boulder-clay to the chalk in this immediate neighbourhood and in many pits round Norwich, I feel no hesitation in concluding that the disturbance was produced by the agent which formed this Boulder-clay." Similar disturbances have been reported by Mr. Wood at Litcham.
Mr. Woodward elsewhere describes a pit showing much disturbed chalk near Burham Abbey, chips of flint and flint nodules occurring in the mass of the rock, the disturbance reaching to a depth of ten feet. At West Rainham the Chalk shows signs of disturbance in an anticlinal arrangement of the flint layers, the fold trending east and west. (Geology of Fakenham, etc.)
Turning to the very important section at Trimingham, I feel constrained to quote Mr. Clement Reid's excellent description. "North-west of Mundesley," he says, "the beds (contorted series) undulate a good deal, the disturbance gradually extending into the lower deposits and becoming more violent, till at last at Gimingham and Trimingham it affects the solid chalk . . . . The normal position of the Chalk would be below low-water mark; but it has been thrown into a series of undulations which have the effect of raising it above the sea-level. . . . These undulations form definite anticlinal and synclinal folds, having their axes parallel with the coast-line, though minor flexures often obscure the structure where only a small exposure can be seen. The bending has been so violent as to squeeze up a ridge of chalk; of which, judging from the dips on the fore-shore, the two chalk bluffs seen in the cliff seem to be the last remnants." Mr. Reid adds - "That this contortion is of Pleistocene age is proved by the similar disturbance of the overlying beds, and by the intrusion of tongues of Boulder-clay into the Chalk." This view confirms that of Lyell, who, as Mr. Reid says, "was fully aware or this conformity, and gave illustrations of it, mentioned the mixture of Chalk and Boulder-clay on the foreshore, and considered that the contortion must clearly have been formed subsequently to the deposition of the Drift" (Geology of Cromer, etc., p.95).' Again, the same author says: "The Boulder-clay under the folded Chalk is certainly connected with the contortion, as is also the case with the alternations and intrusive tongues of Boulder-clay seen on the foreshore . . . . The contortion of the Chalk appears to have forced it into the. overlying beds and compelled the boulder-clay to mould itself to all hollows and open fissures; it has even in some places caused the Drift to underlie in mass the inverted anticlinal of the solid chalk."
With these facts before us, it seems impossible to doubt the conclusions of Mr. H. B. Woodward and Mr. 0. Reid, as related by them in the following words. The former say.: "I have come to the conclusion that many of the contortions seen in the strata, whether Chalk, Crag or Lower Glacial, are chiefly due to the agent that brought the Boulder-clay; of the numerous cases where this positive evidence is wanting I know of no instance where the contortion might not have been produced at this period" (Geol. of Norwich, p. 137). The latter says: "The general structure of Norfolk and Suffolk appears to show that the whole of the contortions are of one age, that of the greatest glaciation,, or of the great chalky Boulder-clay, and it is probably to this period that the disturbances on the coast may be referred" (Geol. of Cromer, p.117).
While this conclusion seems inevitable, I cannot concede, even as a possibility, that these contortions have been caused by ice in any form. These contortions are, in fact, only subsidiary folds in the much larger folds which formed the plateau of East Anglia and the adjoining troughs on either hand, and seem unmistakably due to the operation of forces acting from below, or by earth-waves passing laterally through the strata as waves pass through the sea.
The only reason given by the opponents of these subterranean causes is, that the surface layers are alone contorted and puckered, while the deeper ones are not. It is forgotten that this very fact is most difficult, if not impossible, to explain by an ice theory, while, if the contortions are eventually due to the crumpling up of the strata, it will certainly follow that the highest layers will be under the greatest tension; but I have a notion that these folds are really the result of gigantic earth-waves, caused by some tremendous strain; and it will be remembered that in marine waves it is only the surface layers that are affected at all; at a very little below the surface the water is quiescent and still.
If we conclude that the disintegration of the Chalk was the result of subterranean movements, the next question is, When did this Occur?
It seems to me impossible to carry back the breaking up of the Chalk strata to Tertiary times. If it had been in progress then in anything at all like the way in which we must postulate it to have occurred, if we are to judge by the lumps of chalk in the Chalky clay, we should certainly find some of these angular and subangular pieces of chalk, some of these great masses of shifted Oolitic and Cretaceous rock, in the sands and gravels of the Crag; but nothing of the kind occurs in them, or in the so-called Chillesford and Westleton Beds. But this is incredible, if the Chalk had already begun to be broken up into this rubble. They come upon us suddenly in the beds above the Crag, and were doubtless the product of the same forces which contorted and faulted and broke the Chalk in so many places, as I have shown. I cannot see how we separate these dislocations from the forces which moulded the surface of East Anglia into its present contour of wold and dale. On this subject we are not entirely wanting in evidence: thus, it is hardly possible to conclude otherwise than that the present depression in the area occupied by the Fens, or the valleys of the Axholme and the Trent, did not exist when these beds were being laid down in the Crag areas, or else we should have had them developed in these hollow troughs more conspicuously than further east. The way in which the later Crag beds themselves occur at high levels above the sea, as at Norwich, and in other inland parts of East Anglia far above the present sea-level, unmistakably points again to the contour of the country having greatly altered since these submarine bed., the very latest so-called pre-Glacial beds, were laid down.
Again, if we travel northward, the position of the Crag beds in reference to the Forest bed points in the same direction. The Middle and Lower Crag, whatever their actual horizon, can hardly be placed above the Forest bed, yet we find in many parts of Suffolk these marine deposits at a considerable elevation above the sea-level, while the Forest bed itself occupies the strand actually below low-water mark. This assuredly points to a considerable dislocation since these beds were laid down. Again, there is another remarkable piece of evidence which has been overlooked that presented by the well-borings at Boston in Lincolnshire, and at Yarmouth and elsewhere on the Norfolk coast - namely, that the great flexures of the Chalk which have rent it down there to a depth of several hundred feet, were clearly made at this time, since the hollows have been filled up with vast deposits of so-called glacial sands, etc., and with nothing else, showing that these synclinal hollows are among the very latest of geological phenomena.
As I have argued, its effect was to fold the Chalk into a series of anticlinal and synclinal curves, running more or less north and south, and marked by the wolds of Yorkshire and Lincolnshire and the plateau of East Anglia on the one hand, and the hollows of the Axholme valley of the Fens and that forming the southern part of the North Sea on the other.
Now this last hollow was clearly cut out and shaped since the Weald denudation. The denuded Weald area was originally lenticular in shape, like similar denuded surfaces in Western England and the Chalk districts of France. The eastern terminal apex of the original denuded area is still to be found on the other side of the Channel. It was athwart this formerly continuous valley of denudation that the great synclinal hollow of the North Sea was shaped or out: a glance at the map will make this quite clear. And this was cut when the connection of England with the Continent was severed, that is, as I have argued in many places, when the Mammoth and its companions were destroyed and tile Drift distributed.
This shows that the bending and moulding of the beds of Chalk in Eastern England into their present contours were comparatively recent events in its geological history, and coincident with the break up aud disintegration of the Chalk beds. If this subsidence and bending had been slow and gradual, we should hardly have had the tremendous breakage and ruin of which the evidence is everywhere most plain. This shows that the breakage was rapid and cataclysmic, and the result of some great strain suddenly applied - such a strain as occurred frequently enough in the earlier ages of the world, as the interior skeletons of all our mountain ranges show, whenever we examine their crumpled, torn, and dislocated beds, often standing on end. It is strange that the moderate Uniformitarians should allow this in the older times, but be loth to admit it so late as Pleistocene times.
The conclusions I have here formulated were foreshadowed long ago by
at least one writer. The Rev. W. B. Clarke, who wrote so well on Suffolk
geology, says in the Geological Transactions for 1837: "While the Crag
still lay under the sea, a violent catastrophe broke up many of the Secondary
rooks, from the Chalk to the Lias inclusive . . . . After this period,
and probably in prolongation of the first great catastrophe, a series of
shocks, acting from below, shattered the surface, and gradually elevated
the whole district, including the Chalk, till the Crag obtained the height
of nearly 100 feet above the sea-level; and by this movement were produced
the valleys or lines of fissure through which the drainage of the country
is effected." (Op. cit. second series, v, pp. 367, 368).