notes on the geology of parts of yorkshire and westmoreland · which the carboniferous rocks lie....

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geology of the country in the immediate neighbourhood of Ripon, which have come under my notice. They are not any of them, perhaps, of any very great importance, yet they serve to fill up a little page in the general history of the earth in past ages.

NOTES ON THE GEOLOGY OF PARTS OF YORKSHIRE AND WEST

MORELAND. BY T. MC. K. HUGHES, M.A., F.G.S., H. M. GEO

LOGICAL SURVEY.

The observations on which these notes are founded were made when carrying on the geological survey of the district, and are now offered to your Society with the permission of the Director of the Survey.

I do not propose to give a detailed description of the district, but rather to call the attention of your Society to points of special interest, which may be visited ia. a summer's day ramble, or points of special diflGioulty, which require working out.

The general features of the coimtry may be thus summed u p . Ingleborough, Whernside, and Penyghent consist chiefly of Toredale rocks, capped by Millstone grit, and resting on a great plateau of Mountain limestone, which slopes gently, with the slope of the beds, to the N.N.E. Under the southern escarpment of the limestone, and in the deep valleys of Horton-in-Ribblesdale, Crummack Beck, Clapham, Chapel-le-dale, and Kingsdale, we find different members of the Silurian series on the upturned edges of which the Carboniferous rocks lie. The Craven faults, of various ages, running nearly W.N.W. and E.S.E., bring down the Mountain limestone on the S. against the Silurian rocks, and again the higher Carboniferous, and even Permian, against the Mountain limestone. As we get near the Lune, a great system of N. and S. faults runs into these, connectiQg

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them eventually with the Pennine system. Taking the rocks in ascending order, we have first:—

The Silurian Hocks. As I have a paper in the press* describing these beds in

some detail, I will now notice only the more important points.

To the lower Silurian we must refer the Green slates and overlying Coniston limestone of Chapel-le-dale, Eangsdale, and Horton-in-Eibblesdale. The Coniston limestone and overlying Trinucleus shales of Sarley Beck and the Rawthey N.E. of Sedbergh, and of Helm Gill, near Dent, and the Coniston limestone and overlying Trinucleus shales and ash-like beds of Austwick. Professor Harkness has shown that the Green slates are on the horizon of the Caradoc sandstone. The Coniston limestone is generally allowed to be the equivalent of the Bala limestone, and the shales with Trinucleus, of Austwick, &c., occur in the same position relative to the Coniston limestone that the Trinucleus shales hold with respect to the Bala limestone of Wales and Ireland.

jQiese older rocks were hardened, upheaved, and folded along axes running nearly "W.N.W. and E.S.E. {i.e., parallel to the Craven faults), and on their denuded edges the upper Silurian rocks were deposited. The proofs of this may be well seen near Austwick, where, on the south side of Souththwaite farm house, there is, at the base of the Coniston Flag series, a bed of conglomerate, made up of fragments of the older series, and resting on shales containing Trinucleus and other marked Lower Silurian forms. The conglomerate occurs again just below Austwick Beck head, where it rests upon shales which I would refer to a lower part of the series than those on which it lies near Souththwaite. It is very calcareous, and in places is represented by a grey, coarse looking crystalline limestone. This is important, as in the next

* Geological Magazine, August, 1867.


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valley, near Crag Hill, S.W. of Horton-in-Ribblesdale, there is no conglomerate at the base of the flags and grits, but there is a similar rough grey limestone resting on the close grained blue Coniston limestone and Shale. Unfortunately I could only find two species of Favosites, which prove nothing in this grey limestone; but they are the same as those which occur in the conglomerate at Austwick. The order of succession of the flags and grits above this is clear enough, and the series is characterised by well marked Upper Silurian forms, such as Cardiola interrupta, Pterinea tenuistriata, &c.

Upon such evidence I wish to return to the classification published by Professor Sedgwick in 1846, and say that, " on the evidence both of mineral structure and of fossils, we are compeEed to separate the Coniston flags from the Coniston limestone and calcareous slates, placing the former at the base of the Upper Silurian series of the Lake district."*

The Old Bed Sandstone and Carboniferous Bocks. The next question of great interest is, what is the base of

the Carboniferous series? Along the cliffs from near Settle to Ingleton the base of the Mountain limestone may be traced resting with an almost unbroken line of jimction on a planed-off surface of Silurian rocks. About Kirkby Lonsdale, Sedbergh, and many other places W. and N., thick masses of Old red, with its coarse drift-like conglomerate, tell of deep valleys filled with the debris of higher land. On the north side of the Howgill Fells, thick beds of red sandstone and conglomerates, alternating with more or less calcareous shales, are evidently the waste of neighbouring land, resorted on the sea bottom, where numerous corals, shells, and other forms of life flourished.

Near Horton-in-Eibblesdale, at Gillet Bree, in Beecroft Hall plantation, and near Dove Cote, we have pockets of a coarse red conglomerate in the surface of the Silurian rocks,

* Wordsworth's Guide to the English Lakes, p. 223.


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and the Mountain limestone, m t h its own peculiar thin beds and conglomerate, seems to lie on this with an even line, as it does on the Silurian rocks on either side. Fossils occur among the fragments of silurian, at the very base of the Hountain limestone. Corals seem to have grown in abundance among the loose stones and on the rocky sea bottom, but no fossil have I ever found in those pockets of Old red.

This will apply also to the larger patches near Kirkby-Lonsdale, Sedbergh, Kendal, and the foot of TJllswater, as far as we can observe them in those faulted districts. At any rate, we may say that the Mountain limestone never rests on an irregular surface; all the old valleys and minor inequalities having been filled with coarse conglomerate previous to the deposition of the Carboniferoujs rocks.

I t would appear from this that we have in the Old red the remains of an earlier formation lying on the irregular surface of an old continent, and small patches were preserved in the deeper hollows when the carboniferous sea planed across it.

But, on the other hand, in Hebblethwaite GiU, near Sedbergh, we find the <5oarse red conglomerate succeeded by shales, grits, and earthy Hmestones; and in these shales a aecond bed of red conglomerate occurs, in every respect similar to that below. On the north side of the Howgill Fells, near Tebay and Shap, there seems to be a clear passage up from the coarse red conglomerate into finer conglomerates, sandstones, shales, and limestones. The shales and sandstones contain remains of plants and marine shells. On the whole, therefore, it seems most probable that, as the land went down in the early carboniferous period, the sea kept planing off everything up to the Lake mountains. Perhaps there was then a more rapid subsidence; at any rate, the sea crept up the hills, and found in the recesses great masses of debris, the result of sub-aerial waste. Some of these got covered up, and are still preserved; others were washed


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out, and resorted over previous marine deposits, or on the bare sea bottom, and from these resorted beds there would be a passage up through the Lower limestone Shale to higher carboniferous beds.

This view wiH quite explain why we seem to have a passage in one place, and in another a sharp line between the Old red conglomerate and Carboniferous rocks.

It would appear probable, from the nimiber and character of the corals and the plants imbedded in the earliest deposits of the period, that the climate was temperate or sub-taropical.

This will not afiect the question next to be considered: whether the Old red conglomerate may not be an ancient glacial drift, as we might then, as now, have in temperate zones a thick glacial drift the record of previoua dimatal conditions.

Professor Bamsay first put forward the view that these conglomerates were of glacial origin, founding his opinion upon the following observations: (1). The manner of their occurrence in isolated patches in old valleys. (2). The character of the deposit, which is a coarse conglomerate, showing a very irregular accumulation. (3). The shape of the included fragments, which is very similar to that of the fragments of the same formations in the glacial drift; and, (4). The occurrence of scratched stones.

But we must remember that any sub-aerial or fluviatile deposit, covered by an encroaching sea, must have that patchy character, that in its irregular accumulation, and the shape of the stones, it more resembles the gravel drift of the valleys than the Boulder clay; and the origin of this gravel drift is, at any rate, doubtfully glacial. I think we must be cautious, too, about referring the scratches on the stones to glacial action—though undoubtedly they are like those found in the true dtift, and the shape of the stones is also the same. Yet they have never been found except


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where we have other evidence that the beds have been much disturbed. We see, where the red conglomerate can be examined close to the great faults, that the beds do not get crumpled up, as in the Silurian or any even bedded homogeneous rocks, but that, because the hard and included pebbles resist more than the soft matrix, the whole mass re-adjusts itself to suit its new position, the included pebbles being often scrunched against one another, scratched, and broken.

In one place I found, incHned at a small angle to the bedding, a face of jointage, on which were strise similar to those on the scratched stones, running across the soft matrix, and included fragments alike. This, of course, leaves it open to suppose that the old red conglomerate may be the wreck of a glacial drift; but as we know of no gravel made up of fragments of similar rocks, which are not directly or indirectly derived from glacial deposits, the arguments from the shape of the stones, &c., cannot, in the present state of our knowledge, go for much.

One point of great interest is brought out by this kind of examination of the base of the Carboniferous series. I t is the enormous break between Silurian and Carboniferous times. The lowest and variable beds of the upper series rest on the upturned edges of all the formations from the Skiddaw slates to the top of the Ludlow rocks, while the Lower old red, which in "Wales is conformable to the Tilestones, is not seen in this part of the country, having been, probably, denuded away. That is to say, we see that formations equalling in thickness the whole of the sedimentary deposits from the base of the Carboniferous to the present time were removed previous to the Carboniferous period; and from the nature and position of the unconformity between the Upper and Lower silurian rocks, the greater part of this denudation must have taken place in the unrepresented time between the Ludlow and Old red conglomerate of the Lake District.


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The break between the Trias and Permian seems hardly equal in amount to many of the subordinate unconformities in the palaeozoic rocks.

May we not, therefore, reconsider the evidence upon which one of our greatest divisions, that into primary and secondary, is founded.

The great change in the Fauna, as a group, and the new conditions implied by the appearance of such rank vegetation, should weigh more than the persistence of a few genera through Silurian and Carboniferous times, and, coupled with such clear stratigraphical evidence, force us to draw our broadest line at the base of the Old red conglomerate of Westmoreland.

The Glacial Drift. I wiU now skip over a great interval, and offer a few

remarks upon the Glacial period, and some phenomena to be referred to still more recent times.

There would appear to be three drifts, distinguishable in sections, though i t is often impossible to trace the boundary between them on the surface.

The lowest is a stiff blue or brown clay—sometimes so hard that it is difficult to pick a bit out with a hammer—^full of stones which are mostly rounded, the larger number striated, not transported from any great distance, though not always derived from rocks in the immediate neighbourhood. The only places where I feel sure of it are in positions where it would be in part protected from glaciers flowing along the present valleys; as, for instance, imder a great thickness of the lighter drift in the deep gorges coming down from the Howgill FeUs, on the north of Sedbergh, and in the deep valley between Lupton High and Farleton Fell, west of Kirkby Lonsdale.

Next there is the common clay drift, which is generally of a looser, more stony character than the last, hangs on eveij


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hill side, and rtnis out in half-obsolete moraine-like masses in every valley. I t varies according to the nature of the rocks on the hill sides along which a glacier, flowing in the country after it had assumed nearly its present configuration, must have come. To trace one, for instance, a great glacier coming down from Ravenstonedale, between the Howgill Pells and Wild Boar Fell and Baugh Fell, crossed the end of G^arsdale, over to Dent, and was split on the comer of Holme Fell, where, perhaps, it scooped out the great hollow called Combe Scar; part went down the Barkin Beck, and part down the Dent and Sedbergh valleys; the hill range called the Riggs being a mere roche moutonnee in its path. We can trace its action all along the north side of Hohne Fell, carving out deep grooves which first coincide with the bedding, then, where the valley narrows, and the glacier was squeezed up, were cut oblique to the beds, and, at the lower end of the ridge, fairly turned over the comer into the valley of the Lune. When the rock has recently been bared, the smaller strive are found to agree with this. At the north* west corner of Hohne Fell, we see them curving over in the same direction as the great grooves I have been describing. At the south end of Casterton Low Fell, the tributaries from the E. and N.E. forced the Barkin Beck branch of the glacier over the low end of the hill. Again, when there waa a glacier coming down into the Lune valley :&om the 2f., the Sedbergh glacier must have pushed it out to the W., and, agreeing with this, we find the valley of tbe Lnne cut lar back opposite the mouth of the Sedbergh valby.

As the climate grew warmer, and t h ^ e glaciers were receding, they left their debris, as moraine matter, scattered over tbe imdulating country they once occupied. Kow, of what is this composed ? and how does the evidence we get from the rocks found in the drift agree with &at derived from the shape of the country and the direction of the striae ?


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If we draw a line from the north side of the Sedbergh valley, over Killington, down by Gatebeck, to Farleton Fell, jugt where, with a free hand, we should draw the outside boundary of a glacier sweeping out from that valley, we find outside that line, blocks of granite from Shap, of pink porphyry from Bretherdale, and other well marked rocks, which must have been transported on the glacier from the north. Within that line we have nothing but what might have come down the Sedbergh valley. Again, Baugh Fell and "Wild Boar Fell are carboniferous, thrown down by a great set of faults against the Silurian rocks of the Howgill FeUs, and so, as we might expect, the debris which represents the eastern moraines of the Eavenstonedale glacier is composed of Carboniferous rocks, while that on the western bank is composed chiefly of Silurian, while at the south end of Casterton Low Fell also, there is a considerable quantity of Carboniferous rocks in the drift. There are exceptions, of course, but they are not difficult of explanation when we remember that there is evidence of a still older drift than that of which we are now speaking; and that, during the period in which these valleys have been again partially cleared out, there was time for many great modifications. Moreover, we do not yet know where these great ice streams started from.

The third drift is the gravel drift of the valleys; some* thing allied to the kames and eskers. In general composition it is exactly the same as the drift last described, except that it has but little clay in i t ; also, it contains very few scratched stones, and on those the scratches are nearly obliterated, as if by subsequent washing and rolling. I t lies in terraces sloping more or less rapidly down the valley, or in mounds which look like the remains of old terraces. I t never runs far up the hiH sides, and as we get to higher ground we find it more irregular in occurrence and more clayey in composition, till often it is impossible to draw a satisfactory line


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between it and the older drift last described. On the lower side we find terrace after terrace, till we get to the modem alluvium. Now, although it is quite possible that some of these terraces may be due to an older formation, a gravelly drift, planed off by the river, it seems far more natural and simple to suppose that we have here the records of a continuous fluviatile action back to the Glacial period; for, as soon as the glaciers began to recede, the streams which flowed from them must have commenced their work, and sudden flushings must have resorted and carried down the mixed moraine debris, leaving it often on steeper slopes than the gentler flowing rivers of modem times can ever form.

In these gravelly deposits we often find deep hollows with no outlet, as for instance the curious hole known as Hollow Basin, or Devil's Punch Bowl, in Underley Park, near Kirkby Lonsdale, and others near the gardens at Underley; and, on a smaller scale, in several places north of Grimes Hni, and near Sedbergh. Looking at the hole in Underley Park, last year. Sir Charles Lyell told me that similar phenomena were produced sometimes by a glacier receding unequally, and so at one time depositing but little moraine matter on a given area, and at another time more, and so, by unequal deposition, hollows would be left. Another way Sir Charles said they have been sometimes produced was by the breaking off of large masses from the end of a glacier, which would take so long to melt, that the glacier would recede too far ever to fill the hole occupied by the fallen ice.

About a mile N. of Austwick, there are some very interesting points connected with glacial phenomena and subsequent denudation. Resting on the mountain limestone plateau of Norber, there are a number of large blocks of Silurian grit, some to twenty or thirty feet in longest- diameter. These have been forced along from beds at a lower level in Crum-mack valley, and left often on a bare table of limestone.


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Now, as every one must have observed who has walked over these limestone hills, the rock is jointed in aE directions, and the water which falls on the limestone, whether as rain, or as small streams, collected on the overlying Yoredale rocks and drift, disappears in the crevices of the limestone. The result is, that there are no streams running over its surface, and all the water which reaches it at any distance from the shale or drift boundary, is the rainfall on that particular spot. "Well, this rainfall has been intercepted by some of the great Silurian boulders, and the result is, that the original face of the limestone has been preserved under them, while all around it has been eaten away by the rain water, and so the boulder stands on a small pedestal of irregular shape, according as the surface has been more or less protected from the splash and wind-blown rain. We can generally see under some part of these overhanging Silurian blocks, and there we find the limestone smoothed, polished, and strongly furrowed and striated down the vaUey. Thus we have the print of the old glacier stereotyped as it were in the solid rock, and one good fact clearly recorded to help us to work out the history of the past.

Another question which naturally suggests itself is, how much of the limestone has been thus carried away by the rain only, and of course the height of the limestone pedestals above the surrounding part gives us a measure of this. I t appears to be generally from twelve to eighteen inches. Here, again, we get more data for determining the absolute age of some of these phenomena. Assuming the average periodic rainfall to have been constant, or at any rate to be determinable, and the quantity of limestone removed by a given quantity of rain water to be known, to find how many years have elapsed since this limestone was first exposed to sub-aerial denudation. This glaciation of the limestone plateau probably belongs to a late period of the great glacier which extended from Ingleborough to Penyghent. But, still

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later, as the climate became less severe, the ice was confined to, and kept working down, in the small subordinate valleys of Crummack Beck and the Bibble, where, as in Chapel-le-dale, the moutonnied surface of the rocks in the valley, the rock barrier at the end, so well insisted upon by Professor Eamsay as evidence of glacial action, and the half-obsolete moraines, aU point to the continuance or repetition of similar action on a smaller scale.

One question is raised by an examination of the drift to which I think the above explanation of the glacial phenomena of our district will enable us to give at any rate a plausible answer. Why are there so many scratched stones in the older clay drift, when we find so few in the moraines of the modem glacier. Now to examine this question fairly, let us consider why there are few in the modem moraine. The stones are scratched by being crushed along against the rocky bed and one another in or under the glacier. Therefore, as a large proportion of the stones are carried down on the glacier, and never get in or under it, they never get scratched at all; and, in the next place, as there are always streams in, and issuing from, the end of the glaciers, which roll the stones and obliterate the scratches, a large proportion once scratched get their scratches worn away. Now, under what conditions should we get least of these two causes which reduce the proportion of scratched stones P If we have an ice sheet, and no land above the glacier, there can be no debris to fall on to i t ; or, if the land is so far that aU the debris has fallen into the crevasses, all the detrital matter being in or imder must be liable to be scratched. Also, in such a case, the water which flowed from the end of the ice sheet, or of glaciers so large as to be almost continuous across the country, would collect and flow in the hollows and valleys and the moraine matter left at the end of the small hills, or on their flanks, would escape its action. The nearer the


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glacier approached these conditions, the larger the proportion of scratched stones we might expect. Now we do find evidence of the great extent of the ancient ice streams, and, moreover, see, as before noticed, that the oldest drift of which we know anything in this district, and which contains the largest proportion of scratched stones, lies in the sheltered and embayed parts of the hill country.

ON A SYSTEM OF ANTICLINALS IN SOUTH CRAVEN. BY LOTJIS C.

MIALL, ESQ., CTJKATOE OF THE BEADFORD PHILOSOPHICAL

SOCIETY.

The Carboniferous district of Yorkshire may be conveniently divided into three parts: (1.) the Coal Field; (2.) South Craven, in which the southern type of lower Carboniferous rocks prevail; (3.) the tract north of the Craven Fault, which includes the valleys of the Tore, Swale, and Tecs, with a considerable mountain district in which those streams rise, and is characterised by the complex northern series of strata. The typical northern and southern series may be found in the writings of Sedgwick and Phillips, but I must add two or three explanations to prevent misconception.

1. The two series are not to bo taken as uniform over considerable areas. A distance of two or three miles is often sufficient to produce important variations, and we find the southern series gradually passing into the northern one by the sub-division and increased thickness of the beds. Perfect regularity of deposition is quite consistent with great local variations in vertical sections.

2. In many parts of South Craven, particularly near Skipton, the southern series becomes even less divided than the table would indicate. The limestone shales are represented by a dark, laminated limestone, which passes upwards into black or ferruginous shales, and downwards into the


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notes on the geology of parts of yorkshire and westmoreland · which the carboniferous rocks lie....

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