Quarterly Journal of the Geological Society of London/Volume 32/Observations on the Unequal Distribution of Drift on opposite sides of the Pennine Chain

by John Aitken (1820-1884)

 

21. Observations on the Unequal Distribution of Drift on opposite sides of the Pennine Chain, in the country about the source of the river Calder, with Suggestions as to the causes which led to that result, together with some Notices on the High-level Drift in the upper part of the Valley of the river Irwell. By John Aitken, Esq., F.G.S. (Read June 23, 1875.)

[Abridged.]

For many years past the attention of geologists has been more or less directed to the fact that a marked difference exists in the distribution of drift on opposite sides of the Pennine chain, a difference amounting in some instances to an entire absence of that material on the easterly slopes for many miles from the watershed of the country, and over a considerable portion of its length, notwithstanding that these deposits overspread the great plains of Lancashire and Cheshire in great force, and are found mounting up upon the flanks of those hills on their western sides to very considerable elevations, approaching closely in some cases to the culminating ridge, and in others, where the chain is crossed by intersecting valleys, to some hundreds of feet in excess of the summit-level of these gorges. It would further appear from facts hereafter to be adduced, that although some of these cross valleys attain to only very moderate altitudes, no communication existed during the glacial period of such a character as to permit of the passage of a body of land ice from one side of the chain to the other. Whilst, however, these phenomena have not wholly escaped the notice of those observers who have, more particularly of late years, directed their attention to the surface accumulations of the northern counties of England, allusion having been made to the subject by Messrs. Binney, Tiddeman, Green, Foster, Dakyns, Goodchild, and others, yet no serious attempt has, I believe, so far been made to grapple fully with the subject by any of those who have hitherto given attention to it.

The subject has long perplexed me, amongst other observers; and it is only after a lengthened consideration that I have ventured to suggest a theory which, whilst offering an explanation of the phenomena, does no violence to any of the well-established principles of physical or geological science. My object, then, in presenting the present communication is to show that the whole of these phenomena are explicable on the supposition that, during the flow of the great ice-sheet over this region, these intersecting channels were sealed and blocked up so effectually as to completely cut off all communication between the eastern and western sides of the chain, and that the only agency fully meeting the requirements of this supposition is that of ice or snow so consolidated and fixed in the sinuous channels as to remain stationary and inert while the great mass of glacial ice, in two sheets separated by the more elevated portions of the great anticlinal range, traversed its eastern and western sides on its march from north to south.

That vast masses of drift deposits overspread the wide plains of Western Lancashire and adjoining counties, extending from the Irish Sea in one unbroken sheet to the slopes of the Pennine Hills, and thence mounting up to higher levels, and penetrating almost every upland valley and mountain-gorge to considerable elevations, is too well known and too generally acknowledged to require any amplification from me on the present occasion.

A great number of facts, and the statements of various authorities as to the altitude of high-level drift on the western slopes of the Pennine chain, indicate a general elevation of from 1100 to 1200 feet, whilst scattered boulders and pebbles of travelled rocks may be detected at various places in the locality some 200 feet in excess of that; and I contend that these more elevated stray boulders and pebbles owed their origin to icebergs during the interglacial period, and not to the period of land ice.

I wish particularly to direct attention to the circumstance of drift having been found at an elevation of 930 feet above sea-level, on the shoulders of the hills on both sides of the southerly termination of the Walsden defile at the summit near Littleborough, whilst all traces of them vanish in a line almost coincident with the watershed of the valley, which has an elevation of 627 feet, beyond which no accumulations of this character are met with in travelling cast for a distance of about 15 miles. The first indication of their presence as a regular bed of drift occurs in the valley of the Calder at North Dean, near Halifax, where, in sinking for the foundations of a railway viaduct, the following section was observed by Mr. James Spencer, of Halifax, to whom I am indebted for the accompanying particulars:—

	ft.
Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	1
Fine alluvial sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	8
Gravel derived from local rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	2
Gravel containing granite, trap, slate, and Silurian rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	3
	—
Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	14

It is, however, stated that an occasional pebble foreign to the district has been noticed in the bed of the river Calder, a little further to the west than the spot just named^[1].

Close to the railway bridge at Elland, in the bank on the south side of the river Calder, under about 5 feet of sandy loam, a bed of gravel exists, about 4 feet of which is exposed, and which I am informed by Mr. Davis, F.G.S., of Greetland, has been proved by a well-sinking to be from 15 to 20 feet in thickness, in which red granite, silurian porphyritic greenstone, and other foreign pebble's occur; and at and below this point examples of these rocks may be detected in the bed of the river wherever gravel is exposed. This is situated at an elevation of about 200 feet above the sea level.

At the Elland railway-station, the following section has been exposed by some recent operations of the Company:—

		ft.	in.
Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		1	4
Fine subangular gravelly surface wash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		2	6
Loamy sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	6 inches to	1	0
Fine sandy gravel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		2	6
Gravel coarser than that above; stones all waterworn and much abraded, of local origin, resting upon a bed of Carboniferous shale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		5	0
		———
Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		12	4

At the cemetery, a few hundred yards to the north-west of the last-named place, and at an elevation of about 300 feet, a bed of gravel, sand, and loam, varying in thickness from 5 to 10 feet, analogous in character to the section last described, reposes upon the Carboniferous shale. And in the Shibden valley, deposits precisely similar to these are found at about a corresponding elevation.

In the three last-named instances the stones composing the gravel consist of well-rounded waterworn rocks, derived exclusively from the basin of the Calder and its tributaries, not a foreign pebble being found incorporated with them. This gravel may therefore be regarded as having a purely local origin, and probably dates from the time when the river ran at this level, and is consequently in no way connected with the glacial drift which occurs in the valley below.

Precisely analogous conditions to those already described as occurring in the Walsden defile exist in the Cliviger valley, the drift running up on the sides of the hills near the entrance of the gorge to a height of 1075 feet, its southerly termination taking place both on the sides of the hills and in the valley in a line almost corresponding with the summit-level of the latter at Calder Head, which has an elevation of 768 feet.

It appears from a paper^[2] read some time ago by Mr. R. H. Tiddeman, of the Geological Survey, that a very similar state of things occurs with regard to the distribution of drift in the great watershed of the north, opening between the basins of the Ribble and the Aire, which has a summit-level of 700 feet. No ice-scratches are shown on the excellent map which accompanies that paper as existing east of the watershed of the Pennine range in that part of the country; and those which do occur near to that line run, with one exception, in a direction closely approaching to north and south.

In the southerly portion of the chain the behaviour of the drift in the neighbourhood of Castleton (a town situated just beyond the central axis, on the easterly slope of the range) entirely corresponds with the instances already adduced; and this is confirmed by the following quotation from a paper by Prof. W. B. Dawkins^[3]:—"From what I can see, there is nothing whatever in this deposit to separate it from the superficial deposits in the valley near Castleton, which you will find pretty well everywhere. When I examined these the other day in the company of Mr. Prestwich and Mr. Tiddeman, we came to the conclusion that they are not glacial, but the result of subaerial wear and tear of the rocks in the neighbourhood." These examples will, I trust, suffice to show that over this large area, extending from Skipton in the north, by Todmorden, to Castleton in the south, a general absence of drift deposits and of all other indications of glacial action characterizes the eastern slope of the great axial chain in this division of the country, thus establishing the first part of the proposition with which I set out.

We may now inquire if there is any legitimate reason for supposing that drift was at one time deposited over the now barren area, and that its absence at the present time is to be accounted for by subsequent denudation, as suggested by Mr. Tiddeman in the paper previously referred to. It appears to me, from a full consideration of all the facts, exceedingly problematical that this can have been the case; for it is difficult, if not impossible, to conceive of any known force which could act in so capricious and anomalous a manner as to have swept and cleared off the surface of the driftless area to the east so completely that not a trace of its former existence should remain, even in the deep sheltered valleys which intersect the district in all directions and thus present conditions of the most favourable character for its preservation, and yet at the same time leave intact the vast bodies of drift which so completely envelop the country to the west.

The drift found in the lower reaches of the eastern valleys was probably derived from the section of the great ice sheet which traversed that side of the country; and its presence there is no indication of its having been carried through the cross valleys from the west.

Having so far endeavoured to prove, and, I hope, successfully, that a marked difference exists in the distribution of drift on the two sides of the Pennine chain, it now remains to show that this phenomenon has in all probability been induced by the valleys in question having been blocked up during the glacial period by accumulations of ice or snow held firmly in their places by the physical and other characters of the gorges themselves, acting in combination with the force exerted by glaciers pressing against the ends of these blocked-up channels, thus effectually holding stationary the imbedded masses in the places of their deposition.

For a full and clear comprehension of this subject, it will be necessary to glance at the physical and geographical features of the district and to trace their relation and bearing to the surrounding country. In treating of this branch of the subject, our attention will be principally directed to that part lying between Burnley and Littleborough on one side, and Todmorden on the other—a district embracing the deep valleys of Cliviger and Walsden, in which are contained the two lowest watersheds in the whole of this central range of hills.

If, then, we take Todmorden as the central point of the district, from which to commence our observations, we shall find that that town is situated almost on a line with the highest summits of the Pennine Hills, in a deep gorge at the junction of the two streams which flow through the two defiles already mentioned, and on the main axis of that series of dislocations known as the great Pennine fault, which run in a line roughly coincident with the Walsden and Cliviger valleys, and the effect of which has been, not only to fracture and break up the rocks to a marvellous extent, but also to cause a reversal in the dip of the strata, those on the east dipping at an angle of about 5° to the S.E., and those to the west declining at an angle of from 20° to 45° to the W.S.W.

Starting from this centre, three valleys radiate in different directions, in lines almost equidistant from each other:—one stretching off through Walsden to Littleborough for a space of about 5 miles in a direction a little W. of S.; another taking a N.W. course through the sinuous gorge of Cliviger to Burnley, a distance of about 8 miles; whilst the third, the valley of the Calder, takes an E.N.E. direction.

The appearance thus presented, when traced on a geological map, reminds one forcibly of the device which characterizes the Manx copper coinage. By an examination of these arms, we shall find that they are three deep, narrow, rocky, tortuous channels, hemmed in on every side by massive walls of rock, cut into at intervals along their course by the entrance of tributary streams.

The watersheds of the Walsden and Cliviger valleys are at a comparatively low level, that of the first having an altitude of 627 feet above sea-level, and being eaten into to a depth of 330 feet below the shoulder, or first platform bounding the valley^[4]; whilst that of the second is crossed at an elevation of 768 feet, and is excavated to a depth below the immediate country of 475 feet, a depression which would be greatly increased if the summit-level of the surrounding hills were taken as the datum-line for measurement.

The valley of the Calder, which forms the line of drainage through which the waters of the aforesaid tributary valleys, from their junction at Todmorden, pass off to the German Ocean, is cut in to a depth considerably in excess of those already described.

If, then, we view these valleys in relation to the initial period of their formation, structure, and physical characters, the total absence of drift or other indication of ice-action within their boundaries, or the marked contrast presented in the configuration of these and other valleys in the neighbourhood, and the general surface-contour of the surrounding district as compared with the country on the western slope of the chain immediately beyond the watershed, where ice is known to have been, and where the hills and dales lose their stern angular character, and become characterized by a soft, rounded, and flowing appearance, indicating unmistakably the operation of divergent forces, and the existence of wholly different conditions, we shall have no difficulty in concluding that glacial or land ice has had no share in their formation or subsequent modification, but that they owe their origin in the first instance to the fracturing of the rocks, and subsequently to the operation of subaerial forces.

Having now pointed out the physical features of the district, I shall proceed to offer some reasons for concluding that during the glacial period these lines of communication were blocked up by snow or ice so as to cut off all connexion between the two sides of this chain of hills. On the approach of the long winter which preceded the period when ice overspread the county of Lancaster and the whole of the northern part of our island, the severity of the climate would gradually increase; and during this time large accumulations of snow would take place, and ice be formed in deep and sheltered situations like those presented by the Walsden, Cliviger, and Todmorden valleys. The snow, thus accumulated to a depth of from 80O to 1000 feet, would, by being partially melted and recongealed, become in time a consolidated compact mass, little if at all inferior to that of ice itself in density and consistency.

Accepting, then, this proposition, we shall have no difficulty in concluding that these bodies, held firmly in their places in the tortuous serrated valleys which are so constructed, and holding such relations to each other that any attempt to move on the part of the accumulations in one of the arms would be resisted and counterbalanced by the opposing force of the other two branches, each of which would have a tendency to move in an opposite direction, would thus be able to offer an effectual resistance to the force of the great northern glacier, on its approach so far south, to dislodge them from their strongly intrenched positions,—the resistance to all motion on their part being still further increased by the presence of the glaciers acting upon the terminal portions of the two arms at the mouths of the valleys by which those bodies, if in motion, would have to emerge, with a force equal to that exerted at the northerly end of the Cliviger gorge, where the glacier would seek to effect an entrance therein, thus completely neutralizing each other, and preventing any motion on their part taking place. The progress of the glacier in its journey south being thus arrested by an impassable barrier, at or near Holmes Chapel, in the Cliviger gorge, where the valley suddenly contracts and becomes hemmed in on both hands by massive beds of grit rocks, in some places almost vertical, it is evident that the ice forcing its way so far would be compelled either to move on over the imbedded and stationary mass, or be deflected from its course, and compelled to take a more westerly direction, part of it finding its way over the pass separating the Easden Clough from the White well valley at an elevation of 1170 feet, and passing on east of Deerplay Hill and the high land adjoining into the valley of the Irwell, thence skirting the hilly district east of Bacup and crossing Brandwood Moor, the dividing line between the basin of the Roach and Irwell, and so continuing its course on to Manchester and the great Cheshire plain; whilst another stream of ice would doubtless cross from Burnley into the Whitewell valley by the Wholaw-Nook pass, becoming there confluent with the arm already described, the main body moving off in the direction of Burnley and Accrington, on the westerly side of Hambledon Hill, thence pursuing its course south and uniting with the other streams, finally debouching onto the plains of South Lancashire.

In support of the theory that a large body of moving ice meeting with resistance sufficiently powerful can be either entirely arrested, or its various portions be endowed with varying and diverse motions, we have the authority of the Duke of Argyll, Prof. Ramsay, and Mr. Goodchild, some of whose statements fully justify the conclusion that such was the behaviour of the ice in this instance.

In all probability ice did not overflow the higher hills in this part of the axial range, as is manifested by the absence of all trace of its action upon the surface-contour of the country, and by the fact that there are no remains of morainic or other matter to indicate that it had ever been in those situations.

It may be assumed that the great ice-sheet in this part of Lancashire did not rise to so great an elevation by some hundreds of feet as it is proved to have done further to the north by the observations of Mr. Tiddeman, Mr. J. Clifton Ward, and Mr. Goodchild; and I contend that satisfactory reasons may be given for this variation by taking into consideration the gradual slope of the ground, the waste by melting to which the ice would be subjected in travelling south, and its tendency to spread out and become diffused on reaching the flatter and more level plains of Lancashire and Cheshire.

Statements contained in the memoir by A. H. Green, C. Le Neve Foster, and J. R. Dakyns on the Geology of the Carboniferous Limestone, Yoredale Rocks, and Millstone Grit of North Derbyshire and the adjoining parts of Yorkshire, confirm many of these conclusions arrived at by me on independent grounds.

I have thus endeavoured to lay before the reader such facts as have come within my reach tending to illustrate the question forming the subject of this essay, with what success he will be able to judge. If, however, the facts and arguments should fail to carry conviction, I trust that the effort I have made to solve this somewhat difficult and perplexing question may not prove altogether fruitless; for should no other result follow than that of attracting the attention of other observers to the subject, so that eventually a satisfactory solution may be arrived at, my object will, at all events to some extent, have been attained.

1. Dr. Alexander, in describing the geology of the parish of Halifax, in the 'Tracts' of the Geological and Polytechnic Society of the West Riding of Yorkshire, 3rd June, 1841. p. 201, mentions that "in prosecuting the works on the line of railway some blocks of granite had been found near Hebden Bridge;" and Mr. Binney also informs me that he has seen foreign pebbles at Hebden Bridge.
2. "On the Evidence for the Ice-sheet in North Lancashire and adjacent parts of Yorkshire and Westmoreland," Quart. Journ. Geol. Soc. for Nov. 1872, p. 478, a contribution the value of which it is difficult to overestimate.
3. Trans. Manchester Geological Society, vol. xiii. p. 124.
4. Prof. Hull, Geol. Mag. vol. iii. p. 475.