51

CHAPTER VI.

THE YOREDALE ROCKS AND MILLSTONE GRIT (continued).

Eastern District.

(1.) The valley of the Derwent from Ashopton* on the north to Eyam* and Stoney Middleton† on the south.

In this tract the whole series of beds from the Rough Rock down to the lowest division of the Yoredale Group comes out to day.

The black shales of the lowest Yoredale Group are seen in the valleys of the Derwent near Hathersage and to the west and south of the tableland of Abney Moor.

The representatives of the Yoredale Sandstones reach a greater thickness between Hathersage and Hope than anywhere else over the country described in the Memoir; but they seem to thin away on the southern part of the district.

The outcrop of the Shale Grit runs out from the great plateau of that rock which has been already described along the eastern slope of the Derwent valley to below Hathersage. It there crosses to the west of the river and the rock forms a broad spread on Abney Moor.

The escarpment of the Kinder Scout Grit runs on with undiminished grandeur as far as Ashopton. South of that spot the lower bed of this grit thins away at the south end of Bamford Edge: the upper bed runs on, but it becomes finer in grain, and is a far less striking rock than over the country to the north. The Rivelin (or Chatsworth) Grit comes on to the east and makes a series of magnificent escarpments: it is in this district that this bed bears its most typical and conspicuous character. The finer sandstones of the Middle Grits and the Rough Rock follow in order.

Section No. 3, Plate I., illustrates the geology of the northern part of this district, and Horizontal Section, Sheet 70, crosses the southern part. By working from west to east we shall describe the rocks nearly in the order of their formation; we will therefore start with the valleys of the rivers Noe and Derwent, from Hope and Yorkshire Bridge, down to Hathersage.

The sections given by the river Noe between Hope and Brough are mainly in black shale, which may belong to the upper part of the lowest Yoredale group. These beds pass under a series of shales and thinly bedded sandstones, well laid open between Brough and Mytham Bridge, which lie below the Shale Grit and above the lowest Yoredale_group, and must therefore be the equivalents of the Yoredale Sandstones. Except in Edale this group has nowhere been found in the country described in the present Memoir so thick as it is hereabouts, and it seems to thin away to the south, for, with one doubtful exception, it is never seen again in that direction. In the river Derwent, between Yorkshire Bridge and Bamford, the sections are in black shale, very much disturbed and faulted; about Bamford we come upon what are certainly the same beds as those just described in the river Noe, and therefore Yoredale Sandstones. They are well laid open at Bamford Mill, and sections may also be seen in them going up the hill towards Bamford Clough, and in Hurst Clough; their thickness here cannot be much less than 300 feet. Many sections in the same beds may be seen between Mytham Bridge and Hathersage; and we also get evidence for a line of fault, which we may as well give at once. At Sicklehome there is much disturbance and a very sharp † In Map 81 S.E.

* In Map 81 N.E.

anticlinal, and one mile lower down the river on the line of this anticlinal produced the fault itself was seen; the north wall was formed by a bed of sandstone almost on end, while on the south side the dip was more gentle, but increasing rapidly as the beds approached the fault. That it was a fault and not a mere anticlinal was shown most beautifully, thus: on the south side the beds of hard sandstone stood up out of the shales and formed little reefs across the river, and these one after the other ran up and stopped off against the wall of sandstone on the north side. The line of this fault produced eastwards, runs to Hathersage Booths, where there is a fault in the escarpment of the Kinder Scout Grit. To the west it passes through the broken ground at Sicklehome, and then by a little bend through disturbed beds seen near Shatton, and on to a fault in the Mountain Limestone at Small Dale; the latter part of the line is conjectural.

From these sections, and from the distance between the base of the Shale Grit and the river, we conclude that between Bamford and Hathersage, on the north side of the valley of the Derwent, the Yoredale Sandstones reach a thickness of from 200 to 300 feet. On the south side of the valley there is a section given by the brook through Dunge Wood, and here they do not seem at first sight to be anything like so thick, for at the junction of the brook with the Derwent we find black shales with limestone nodules, apparently belonging to the lowest Yoredale group. The base of the Shale Grit here is, however, very ill-marked, the rock gradually passing down into a mixture of shale and sandstone, and where the black shales are seen there is a very high dip, so that they may be brought up by a fault.

The black shales with limestone nodules were again seen in the lower part of Hood Brook, half way between Hathersage and Nether Hall. The nodules contained Goniatites in great plenty with Posidonomya Gibsoni and Lingula mytiloides, and there could be little doubt that here at least we had beds belonging to the lowest Yoredale group.

We may now pass to the Shale Grit, a belt of which crops out along the east side of the valley of the Derwent.* The rock has its usual character, sandstones, here and there coarse, with irregular masses of interbedded shale. The lower boundary is for the most part well given, though where the Shale Grit passes gradually into the Yoredale Sandstone group, as is sometimes the case, the line between them comes arbitrary. The upper boundary is much of it conjectural. The fault laid down crossing Hurst Clough north of Lee Coppice has been drawn because, though the Shale Grit is very distinctly traceable on both sides of the valley, and ought therefore to be seen in the brook itself, we find nothing but shales, with a few thin sandstones, where the line of its outcrop ought naturally to cross the stream; and this can only be explained by supposing the rock to be thrown down to the north by such a fault as is drawn on the map, or by the very unlikely hypothesis that this thick mass of sandstone passes all at once into shale with a few thin beds of stone, and then in a distance of less than a quarter of a mile returns as suddenly to its former shape.

The rock is quarried on either side of Hurst Clough, and is also well seen in a quarry by the roadside a little to the south-east of High Lees. The face here exposed is about 50 feet high, the lower 18 feet being all sandstone, and the rest sandstone with beds of sandy shale. The sandstone is very markedly current-bedded, and micaceous, so that it splits into flags and tiles, the former ranging from an inch and a half to three inches thick, the latter averaging about half an inch. In another quarry, west of the "i" in High Lees, there were good instances of the interlacing of shales and sandstones, a vertical section showing a fan-shaped arrangement of the beds, which widen out from north to south. Besides these sections the rock is well shown in Hood Brook and the stream between Mitchell Field and Hathersage. It may be traced on to the fault through Sicklehome which has been just described.

There are no sections to fix exactly the spots where the upper and lower boundaries of the Shale Grit cross the Derwent, but to the south of the river the rock spreads out and forms a tract of high ground, in the middle of which is the hamlet of Abney. The lower boundary of the rock is well given by brook-sections, and by the shape of the ground, which mostly shows a double escarpment above the boundary, owing to the presence of a shale band

* In Map 81 N.E.

about 15 or 20 feet thick, whose outcrop is marked by a little terrace running between the steep escarpments of the sandstones above and below it. A like band of shale has been already noticed elsewhere in the Shale Grit. A fine section of the rock is given at Bar Tor, where a large landslip has laid bare a vertical cliff; good sections are also yielded by the stream through Dunge Wood and by Highlow Brook; the latter divides a little above Highlow Mill, and the southern branch cuts down to the shales and sandstones beneath the Shale Grit, a long inlier of which stretches for some way along the valley, the beds rising from each side gently towards the middle. Along the south bank of the stream are many landslips, such as are found so frequently along the line of junction of the Grit with the underlying shales where the beds dip into a valley. A strip of Shale Grit runs southwards from this tract, forming a steep ridge to the east of Eyam and Stoney Middleton.

The measurements we have of this rock, if they are trustworthy, show that its thickness is here very changeable. About Abney it cannot well be less than two or three hundred feet thick; in the shaft of the Lady Wash mine there are said to have been 466 feet of it, while an old plan of Stoke Sough in the office of Mr. Aston of Castleton made it 200 feet thick. Between Eyam and Stoney Middleton it is most likely not more than 80 feet thick.

Not a single section was seen in the shales between the Shale and Kinder Scout grits, and the upper boundary of the former is therefore conjectural.

We now pass to the Kinder Scout Grit. Along Derwent Edge* we have a magnificent escarpment of this rock, crowned by many strangely shaped piles of rock, and mostly ending on a cliff of gritstone, below which is a steep slope of the underlying shale.

The rock continues to form a fine ridge down to Ashopton and along Bamford Edge, and an immense landslip, or rather group of landslips, worthy of special notice, occurs above Ashopton Inn. From Crow Tor down to the turnpike road the whole flank of the hill, over an area of probably as much as 30 acres, is thickly strewn with huge slipped and tumbled masses from the cliffs above; not merely large blocks, but masses of rock that must have settled down bodily into their present position. The ground is too much overgrown with timber and too much cultivated to allow any details being observed which would throw light on the formation of the slip, but, from its size, it is perhaps the most impressive instance to be found anywhere in this neighbourhood. At the south end of Bamford Edge the Lower Kinder Grit dies away altogether very suddenly, and the upper bed undergoes considerable change, shale and sandstone beds being mixed up with the grit, and the whole mass being, in places, finely grained sandstone.

Before giving the details of this change we will describe the evidence for a fault running east and west past the Hurking Stones.*

The Rivelin Grit is shifted at Upper Reeves Low: the escarpment of the Upper Kinder Scout Grit is cut off at the north end of Hordron Edge, and the fault itself seen in the brook a little further to the west; and the shales between the two Kinder Grits, which are seen in High Shaw Brook, would abut against the Lower Kinder Grit but for this fault. Hence westward matters are doubtful, but a fault having nearly the same direction, but an opposite throw, crosses the escarpment of the Lower Kinder Grit at the Hurking Stones, points to some very contorted beds in the Derwent, and may thence run to a fault seen in the Ashop near Grimbo Car, and on to a fault in the lower part of Jagger Clough.

We may now turn to the Lower Kinder Scout Grit. The rock is laid open and its base very clearly shown in Lady bower Brook, and in the side of the valley here there cannot be less than three or four hundred feet of grit. The cliff marking the outcrop of the bed is very clear up to the southern end of Bamford Edge; here the rapid narrowing of the ridge, which is well shown by the shading on the Ordnance Map, leads us to look for a change in the rock of which it is formed.

* In Map 81 N.E.

N.

On looking carefully at the cliff we see that each of the different beds in the gritstone mass makes a little subordinate escarpment of its own, and as the eye follows these along the steep flank of the hill, two at least may be very distinctly seen to grow fainter and fainter, and at last die away altogether. The diagrammatic sketch in Fig. 15, which it is hoped will explain this appearance, has been made purposely stiff and formal, and shows what would be seen, if the débris were cleared from the flank of the hill, rather than the somewhat faint hints given by the cliff itself. It will be seen that while on the left hand there are four beds of gritstone, each making a step of its own in the escarpment, two of these beds thin away, and at the extreme right only two are left and the escarpment has only two steps. Thus we get our first suspicions. A little further on we see the upper boundary of the grit in a quarry, and without making any accurate measurements we see at once that the rock here is by no means so thick as in Ladybower Brook; still further on the road from Bamford to Bole Hill crosses what would naturally be the line of outcrop of the rock, and shows only a few feet of coarse grit with a considerable thickness of shale, both above and below it. The line of this rock would run on to the "Slate Pit" marked on the map, and the flaggy sandstone seen there would seem to be the last trace of the bed. All this evidence points to a thinning away of the bed, unusually rapid no doubt; but it did not seem possible to explain the facts observed in any other way, and, moreover, south of this point we never again find any trace of a lower bed of Kinder Scout Grit. The fault already mentioned as crossing the upper part of Hurst Clough would, if produced, run along the southern end of Bamford Edge, and may be in part the cause of the abrupt change in feature there noticed.

Fig. 15.

Diagram to show the thinning away of the Lower Kinder Scout Grit on Bamford Edge.

We will now notice in detail a group of sections showing the beginning of a change in the Upper Kinder Scout Grit, which we shall see as we go further south ends in that rock dying away for a while altogether.

The Upper Kinder Scout Grit forms a second escarpment above Bamford Edge. The base of the rock and the shales between the two grits are well seen beside the Glossop and Sheffield road and in Jarvis Ciough. The top of the rock was seen by Moscar Toll Gate, but hence southwards for three miles the shape of the ground is our only guide in drawing the upper boundary.

About Bole Hill, where the lower bed thins away so rapidly, the upper also begins to fall off in thickness and coarseness. We see this at the Slate Quarries on Bole Hill, where beds which must belong to the Kinder Grit are fine and thinly bedded enough to be worked for tilestones. At a quarry by the "d" of the word "Golden" the rock again becomes coarser, the grains being about the size of wheat; it is here rather felspathic, and contains fossil plants: east of the Paper Mill the rock is pretty much the same in character, but still forms a good cliff at the outcrop. Some quarries three quarters of a mile north