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CHAPTER VII.

THE YOREDALE ROCKS AND MILLSTONE GRIT-continued.

Southern District.*

This tract is rudely triangular in outline, its three corners being near Ashbourn, Cromford, and Morley. The greater part of it is intermediate in height between the limestone hills on the north and the New Red Sandstone country on the south, and is occupied by beds belonging to the lowest Yoredale Group, with an inlier of Mountain Limestone, between Bradbourn and Kniveton, and an outlier of Shale Grit round Kirk Ireton. To the east the Yoredale Rocks are surmounted by the Millstone Grit, the Kinder Scout Grit running with a fine escarpment along a line ranging from the Black Rock, near Cromford, to Little Eaton. A plateau, sloping gently to the east, formed of this rock and capped here and there by outliers of the Chatsworth Grit, occupies the rest of the district, which is bounded on the east by a line of faults, throwing out of sight the Upper Millstone Grits and bringing in the Lower Coal-Measures on the further side.

The rocks therein shown are as follows:

The Chatsworth Grit is a reddish sandstone, not very coarse. The Kinder Scout Grit varies a good deal, being sometimes very coarse and even a conglomerate, and at others a hard closely grained gritstone, only moderately coarse. It is always very thickly bedded. The Shale Grit is also very changeable, at some spots perhaps wanting altogether: it is for the most part a finely grained sandstone, sometimes thickly bedded, with shale. The shales with black limestones have mostly their usual character, but here and there the limestones become so thick, pure, and numerous, as to be worth quarrying for burning into lime. Among these beds, toadstones, which are possibly intrusive, are found near Kniveton.

Section No. 1, Sheet 60, crosses the northern part of this district, and the Section No. 7, Plate I., will explain the structure of the country further south.

To the north of Ashbourn, though the country is much covered by Drift, sections of the Yoredale beds may be found in brook-courses and elsewhere. One of the best is laid open by some quarries north of Fenny Bently. The limestone beds are here numerous, and run close together; they are flaggy

*Lying in Maps 72 N.E. and 71 N.W.

and evenly bedded, and serve admirably for rough unmortared walls, and have been burnt for lime.

Four miles to the north-east of Ashbourn, between the villages of Bradbourn and Kniveton, is an inlier of Mountain Limestone. Drift and the contorted state of the beds make this at many points a very doubtful bit; the conclusions arrived at will be best understood from the map and the section No. 7, Plate I., but we notice a few details of interest.

The upper beds of the limestone are thinly bedded and somewhat earthy, with partings of shale, but chert is not so plentiful in them as at some places. They were well shown in a quarry a quarter of a mile east of New House, where their junction with the underlying, thickly bedded, white limestone was laid bare; also in quarries to the east of Bradbourn, and at other spots. On the western side of the outlier a bed of toadstone is found, whose probable place is between these thin limestones and the more massive limestones beneath. It seems, however, to be wanting on the east, for neither on the east of Wigher Low, nor at any points still further east where its outcrop ought to occur, were any traces of it found. It is, however, just possible that the toadstone, instead of directly underlying the thin limestones, is parted from them by the massive beds of Wigber Low, and is not brought out to day on the eastern part of the inlier.

The boundary of the inlier on the west is a fault, which at one spot brings the toadstone against Yoredale shales. On the north a similar juxtaposition, south-west of Lee Hall, shows the boundary to be there a fault, but as we go towards Bradbourn the fault seems to die out, and at that village the upper linestones may be seen passing regularly below the Yoredale shales. Between this village and Whin Barn the limestone is thrown into many sharp saddles, and the boundary is partly a natural one and partly formed by small faults. From Whin Barn by Over Hall Fields, round to the north of Kniveton, the ground is covered by Drift, and the boundary to a great extent conjecturai. Two of the faults marked at Standlow were seen in a quarry, and are shown in Fig. 23.

S.W.

Fig. 23.-Section at Standlow, north-east of Kniveton.

N.E.

2

1. Massive white limestone

2. Thinly bedded limestone with a little shale
3. Black shale with thin limestones

-Mountain Limestone.

Yoredale Rocks.

Hence the boundary for about half a mile is a natural one, broken by faults. The fault through Kniveton Wood is necessary to explain the relative position and dips of the limestone and Yoredale beds on opposite sides of the valley. The latter besides the usual thin limestones contain here some beds of chert.

Half a mile south of the village of Kniveton are two outcrops of toadstone among the Yoredale beds. The section and plan in Fig. 24 will show their lie. It is clear from these that the lines marked x x x must be faults or that the toadstones must be intrusive. Sir A. Ramsay considered the latter view the safer.

The limestones interbedded with the Yoredale shales are here unusually thick and numerous. This is also the case near Over Hall Fields, about a mile to the south-east, and also north of Hognaston; in both places they have been largely quarried, and at one time burnt for lime. The proportion of shale to limestone is, however, even here far too great to allow of this being now done with profit.

The outlier of Shale Grit round the village of Kirk Ireton requires little description. The base of the sandstone is well marked all round, except at the south-west corner, where some large knolls of Drift-gravel hide the boundary. There are several large quarries on the northern edge, and others a mile north of Kirk Ireton, and again on the hill called the Mountain on the south of the village.

Fig. 24.-Plan and Section to show the lie of the Toadstone south of

Some good sections in the Lower Yoredale beds were given by the cuttings of the Duffield and Wirksworth Railway, near the latter town. The black shales were often hard and slaty, probably owing to a calcareous cement, and contained in plenty Goniatites and Aviculopecten papyraceus of large size.

The only other section of importance before reaching the ridge formed by the Kinder Scout Grit is given by the limestone quarries, one mile south of Turnditch. The Yoredale limestones are here unusually numerous, thick, and close together, and are still largely quarried for wall-stones and burning into lime. The "head" of shale is now getting too thick to allow of the stone being any longer raised in open work, and the quarries are struggling on by following the better beds in underground galleries driven on the dip. Owing to the absence of every one connected with the works at the time of our visits, we did not learn whether the stone possessed any qualities valuable enough to make this method of working profitable.

To the south of the country just described, the floor of Carboniferous rocks, on which the New Red Sandstone rests, has been laid bare at several spots by the denudation of the newer rocks.

The largest and most notable of these inliers lies on the north side of the village of Kirk Langley. In its south-eastern part we find the ordinary black shales and limestones of the Yoredale Group, but towards the north-west these beds are overlaid by a mixture of hard, closely grained sandstone and shale. The sandstones are not very like Shale Grit, but do in some degree resemble the Yoredale Sandstones of North Staffordshire. It is odd that representatives of these beds, which we have so long lost sight of, should turn up in so unlooked-for a way, but the likeness is strong enough to lead us to think that the rocks in question really belong to this group, and that the area which the Yoredale Sandstones originally covered reached at least as far as this spot.

The broad spread of Yoredale Rocks which we have just gone over, is bounded on the east by a ridge formed by the combined escarpments of the Shale Grit and Kinder Scout Grit, to which we will now turn our attention.

Shale Grit.-A large irregularly lenticular mass of sandstones and shales reaching from Little Bole Hill on the north to Handley Wood on the south, apparently thinning out both to the north and south, so that its lower boundary merges into that of the Kinder Grit, has been taken as the representative of this rock. The shale-partings are very changeable, and while at some spots we can trace as many as three lesser escarpments, at others the whole mass seems to be sandstone from top to bottom. For this reason also it has been found impossible to draw an upper boundary to the bed, the sandstone in some places seeming to run up to the base of the Kinder Grit, and in others to be parted from it by a variable band of shale. This group of beds seems also to thin away to the east, for we do not find it below the escarpments of the Kinder Scout Grit in the valley of the Derwent. But to the south a sandstone, which may represent it, rises from beneath the Kinder Scout Grit, and runs to Duffield, where it is lost to sight beneath the Alluvium of the Derwent. Northwards the feature made by this sandstone is masked by Boulder Clay, but in parts of the outcrop shown is fairly pronounced, and in default of a better line the bed has been taken as the base of the Millstone Grit.

Kinder Scout Grit.-Starting at Ambergate Station on the large eastern boundary fault, which we will call the Ambergate fault, we find the base of this rock running with a well-marked escarpment along the western flank of the Derwent valley: it winds round towards the Black Rock, near which it is broken by several faults. West of Alport Heights we suppose the rock to be faulted, because the escarpment we traced from Barrel Edge seems to end at the Bent, whilst above New Buildings there is a rock which we could not satisfactorily separate from the Kinder Grit. When the changeable mass of Shale Grit occurs below the Kinder Scout bed, the base of the latter is rendered thereby somewhat uncertain, for though the latter is as a rule the coarser, both rocks consist of a mass of sandstones and shales, forming lenticular beds dovetailed into one another, so that it becomes a matter of uncertainty what ought to be considered the base of the Kinder Grit, and quite impossible to keep on an accurate geological horizon. South of Handley Wood we have again a very good base to the rock down to Camp Wood, because the grit here immediately overlies shale. Between Camp Wood and Morley Moor the

line is concealed by Drift. The rock yields excellent building-stone, and is largely quarried between Cromford and Whatstandwell and south of Milford. On the top of the Kinder Scout Grit there is generally a coal, about eighteen inches thick, which was once worked about Alderwasley and Belper.

The Chatsworth Grit is found only in outliers, of which there are four. We will now give the evidence for the faults which bound on the east the Millstone Grit beds just described.

The Ambergate fault runs north and south from near Milford to Crich. The escarpment of the Kinder Scout Grit may be traced to Ambergate Station and the rock itself seen at several spots between there and Belper. There is, however, every reason to believe that the sandstones on the eastern flank of the valley between Ambergate and Dunge belong to the Lower CoalMeasures, for they appear to pass regularly beneath beds in which known coalseams have been worked, and in mineral character they closely resemble the rocks of the Ganister series and are totally unlike any of the Millstone Grits of the neighbourhood. For this reason a large fault down to the east must range down the valley. One point is given near Bilberry Wood, three quarters of a mile north of Ambergate, where a well-marked bank of sandstone ends off, as if by a fault, against shales. At Ambergate Station the Kinder Grit is thrown against a thickly bedded sandstone, and the two escarpments fit so neatly into one another that the exact place of the fault seems at first sight somewhat doubtful, but on looking at the ground more carefully we note a change in feature which probably marks the position of the break. Again, along Bull Lane and southwards for about three miles a sandstone bed runs with a good escarpment along the eastern flank of the valley. The distance between the bed and the Kinder Scout Grit is too great to allow of this being the Chatsworth Grit, and its mineral character forbids our taking it for the Rough Rock, it must therefore be a Coal-Measure sandstone. The line of the Ambergate fault runs, when produced, through Belper between this rock and the Kinder Scout Grit, and explains the relative position of the beds on either side of the valley. This Ambergate fault may possibly be a prolongation of the Trinity Chapel fault shifted westwards by the Southern Crich fault.

The escarpments of the Bull Lane Rock and of an overlying sandstone end off along a line ranging north-west and south-east through Holbrook, and thus we get the first hint of the fault on the map, which we may call the Holbrook fault. The fault also explains how it is that the top of the Kinder Scout Grit runs down from Chevin House so sharply into the valley. Also on the south-east of Holbrook the coal and the measures on the top of the Kinder Scout Grit are seen, while the rocks between Holbrook and Horsley are Lower Coal-Measures. The fault has been drawn accordingly up to the point where the Kinder Scout Grit seems to end off at Coxbench.

A triangular bit of Coal-Measures half a mile south-east of Milford seems to have been let in between the Holbrook fault and two others. The western one was drawn because there did not seem room for the full thickness of the Kinder Scout Grit; the exact position and direction of the other are uncertain.

A fault proved in the Coal-Measures ranges S.S.E. through Horsley. Along its line produced to the south the Kinder Scout Grit ends off in a marked bank east of Horsley Castle, and a little south of Horsley Park the crop of one of the coals of the Lower Coal-Measures was traced up to within five yards of a large quarry in the grit, the stone of which was shattered and fissured as if close to a large fault. So far then the evidence is good enough. Further south, however, the country is covered with Boulder Clay, and the fault has been dotted on so as to run to the east of all the known sections in Kinder Scout Grit.