The plain to the west of the Penine Hills is everywhere thickly covered with Drift. Drift runs up the slopes of the central table-land, and patches of it and erratics are found on the table-land itself, along its western margin, up to a height of 1,200 feet above the sea. The distribution on the south is nearly the same as along the west side, but the plain is not so completely covered, and the greatest height reached is rather less. The central table-land itself is practically clear of Drift, the only known exceptions being the patches on its western margin, those in the valley of the Wye, and some erratics found in the river gravels of the Yorkshire Calder. Passing to the eastern side of the Penine Range we find a vastly different state of things; for a distance of from 10 to 20 miles from the eastern edge of the central table-land the plain is, with the exception of a few patches of Boulder Clay and a sprinkling of erratics, free from Drift. When further to the east we do reach a country where Drift comes on, we find it thin, and instead of wrapping the country in one widespread covering, occurring only in scattered patches. It seems too that the greater part of the Drift of this region contains fewer foreigners, and is more largely made up of local rocks than on the west.

The comparatively driftless area on the east of the Penine Chain extends towards the north as far as a line which runs about from Leeds to the head of the valley of the Bradford Beck and thence follows in a general way the waterparting between the Aire and the Calder. North of this line Drift is plentiful on both sides of the Penine Hills.

Such, as far as our knowledge goes, are the facts. The explanation of them may be somewhat as follows.

There is very little doubt that much of the material for the Drift on the western part of the Penine Hills was derived from the southern part of the Lake Country and the adjoining high ground of North Lancashire. The natural outlet for the ice from these regions would have been westwards into what is now the Irish sea. But its progress in this direction was barred by a great ice-sheet which descended from the mountains of the south-west of Scotland and advanced southwards over the bed of the shallow Irish Sea, and so it came about that the Lake Country ice streamed down towards the plains of Lancashire, Cheshire, and North Staffordshire, and was pressed up against the western slopes of the Penine Hills.

It is for this reason then that Drift is so plentiful on the west of these hills. And it is reasonable to suppose that this belt of lofty ground would prevent the Drift that took this course from spreading to the east. If we look upon the Boulder Clay of the plains of Lancashire, Cheshire, and North Staffordshire as the product of land-ice, we can well understand that the ice-sheets, though still able to progress over the undulating ground of the lowlands, did not at this distance from their source retain enough motive power to enable them to mount the steep western face of the hill-country. If these Boulder Clays are subaqueous, then these hills formed the shore-line of the water in which they were deposited.

Little or none then of the Drift which came from the southern part of the Lake Country and the adjoining high ground could be expected to find its way across the barrier formed by the southern part of the Penine Range; there is no gathering ground corresponding to that of the Lake Country, and anything like so near, on the eastern side of that range, and it is therefore not surprising to find a good deal of the country to the east of the hills practically bare of Drift.

Thus we may account for the great scarcity of Drift over the plain on the east of the southern part of the Penine Range, but it remains to

explain how the patches that do occur came there. Some of these, the deposit for instance in the railway-cutting near Barnsley, look very much like the product of land-ice, and many of their travelled stones may have come from the Borrowdale series of the Lake Country. But if this is the source to which we may look for their materials, these must have travelled by a different route to that pursued by the Drift on the west of the Penine Chain. Now, it has been shown that the ice, which was shed off from the northern part of the Lake District, and would, if it could, have escaped down the Vale of Eden into the Solway, was met on this side by the ice from Scotland, and was forced to mount the westerly slope of the Cross Fell Range, and flow through the pass of Stainmoor, whence it spread itself out eastwards and southwards.* It looks as if this flow extended itself on the south at least as far as South Yorkshire and North Derbyshire, and the patches of Till which lie scattered over the otherwise driftless plain on the east of the southern portion of the Penine Range may be the relics of its handiwork. They are fragmentary for two reasons. The ice, being near its southern termination, was thin and not able to manufacture much Till, and a good deal of what it did make has been carried away by denudation. The presence of what are probably Lake Country erratics would be accounted for on this hypothesis; we can also well imagine that the ice as it moved southwards would be reinforced by glaciers flowing down the Yorkshire Dales, and these would bring the boulders of Carboniferous Limestone and other Carboniferous rocks which are plentiful in the patches of Till sprinkled over the castern plain. We have then, on the west, plains deeply buried in Drift, huge piles of Drift banked up against the western wall of the Penine table-land, and Drift finding its way up inlets and through gaps in the table-land, because on this side the home from which the Drift came was near at hand, and the ice which brought it travelled by the shortest path possible and was hemmed in and kept on its path by a wall of ice on one hand and a wall of hills on the other. On the east there was no gathering ground anything like so near, the ice came by a long and circuitous route, and was free to spread itself out without hindrance to the east as well as to the south, and so on this side its energies were weakened by dispersion, and its products are small in amount and scattered. The probable course of the ice is shown in Fig. 25, which also indicates that the Lake District ice sometimes forced the Scotch ice northwards, both then passing eastwards towards the Tyne.

This much may be said about that part of the Drift which was made by land-ice. There is besides much on both sides of the hill which was formed under water. This, again, is large in amount on the west, partly because it was formed out of the abundant store of pre-existing Till, and partly because additional supplies continued to be furnished from the Lake Country, and this was near at hand. The reason why the subaqueous Drift on the east is less plentiful is perhaps this. It is formed mainly out of local rocks, and these do not rise into lofty hills, and were therefore broken up by denudation only to a comparatively slight degree.

A word must now be said about the central table-land and the patches of Drift in the valley of the Wye.

The absence of Drift on the table-land, and the fact that only one somewhat doubtful case of glaciated rock has been detected upon it, seem to show that it has never been overflowed by ice. That the ice from the north would not be able to surmount it has been already shown to be probable;

* J. G. Goodchild, Quart. Journ., Geol. Soc., vol. xxxi. (1875), p. 55.

and perhaps it lay too far to the south to be able to nourish an ice-sheet of its own. Small glaciers may have gathered on it, and the "Bloody

Stone" may have been the work of one of these.

Fig. 25.

Map showing the Glaciation of the North-West of England.

As for the patches in the Wye valley we note that these are all found either in the valley of the Wye, or in that part of the valley of the Derwent which lies below the junction of the two rivers, the part of the valley of the Derwent above its junction with the Wye being clear of Drift. This leads us to suspect that this Drift has come from the west along a gap cutting across the great barrier of the Penine Chain. Such a gap can be shown to exist. The valley of the Wye will serve as far as Buxton, where the river is about 1,000 feet above the sea; thence the London and North-western Railway to Stockport runs along a depression whose summit level at Doveholes is not more than 100 feet higher, and descends into the valley of the Goyt at Whaley Bridge, where the ground is less than 700 feet above the sea; the valley of the Goyt will serve for the rest of the way.

A depression of from 1,100 to 1,200 feet would convert this pass into a strait, while it would leave the greater part of the adjoining table-land above water. Under these circumstances it is perfectly conceivable that Drift might find its way through the strait from the west, but none would be deposited on the high ground to the north and south of it. Now the shell-bearing gravels of the neighbourhood of Macclesfield show that during a part of the Glacial Epoch this part of the country was submerged to a depth of at least 1,200 feet, and it was perhaps during this

U 18863.

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submergence that the foreigners found in the Drift of the Wye valley were carried from the west on floating ice. It may be objected that we do not find Drift all along the gap, and specially that there is none at the summit where the water would be shallowest and the chances of an iceberg's stranding the greatest; but we do not know how much has been carried away by denudation, and there may have been a strong current through the strait, the scour of which would, as the land rose, sweep away all the Drift near the summit, and only those patches which lay in more sheltered spots lower down the valley would remain to tell the tale of what has been.

The

The valley of the Calder furnishes another case in which Drift seems to have found its way from the west through a gap in the barrier formed by the Penine Hills. It has been long known that boulders of foreign rocks occur in the river-gravels of that valley.* They were fairly abundant in the excavation for the gasworks at Dewsbury. erratics were rounded boulders of all sizes up to six inches in length; one boulder could not be distinguished from Ennerdale Syenite, and others could be matched among the volcanic rocks of the Borrowdale series of the Lake District. There can be no doubt then that some at least of these strangers have travelled from the west, and it seems not unlikely that they were brought during a period of submergence when the pass was under water, but the hills on either side were high and dry.

The deposits of Drift in which they may be supposed to have been originally embedded have been completely cleared off by denudation, and the only relics of them are these boulders, which on account of their size and hardness have been rounded, without being ground away, as they were rolled down by the river.

We have attributed the transport of the erratics in the valley of the Wye and Calder to floating rather to land-ice, because, as has been already explained, it does not seem likely that the hills across which these valleys run were ever overflowed by the ice-sheets coming from the north.

River Deposits.-Narrow strips of river-gravel are found along the valleys of the rivers Noe and Derwent. For the most part they are above the reach of even the highest floods that occur at the present day, and they must have been formed at a time when the volume of the streams was larger than now, and their fall less rapid; at present the rivers mostly flow in deep channels cut down through their old Alluvia well into the bedded rocks below.

River Noe.-The valley of Edale above Edale Mill† has on the north side of the river a broad flat bottom looking very like an alluvial plain; here and there we find patches of gravel at a little below Edale Mill. The gravel, however, is much mixed up with rainwash, and is not widespread enough to justify us in mapping the whole as an alluvial flat. From Edale End, however, down to Mytham Bridge,† a well-marked strip of gravel is found, showing at times two or more terraces. A good section was seen where the road leading from Hopef to Twitch Hill Farm crosses the stream. The gravel is here of all degrees of coarse

*On the occurrence of boulders of granite and other crystalline rocks in the valley of the Calder, near Halifax. J. T. Clay. Proc. Geol. Soc. of West Riding of Yorkshire, vol. i., p. 201 (1841). Erratic boulders in the valley of the Calder. J. W. Davis. Ibid. New Ser., Part II., p. 93 (1876).

† In Map 81 N.E.

ness down to sand, stratified and false-bedded; in it are lumps and a bed of black clay, evidently decomposed shale. Near the river all the stones are rounded, but as we go up the hill the gravel becomes mixed with angular rainwash, and the two pass into one another so gradually that it is hardly possible to draw a good line between them. The village of Hope stands on the highest terrace, at the foot of which the river now flows, with a steep cliff for its bank, which it is undermining; on the opposite side of the stream the gravels show several terraces.

The valley of the Peak's Hole Water* is somewhat like the upper part of Edale; probably, but not certainly, covered with river-deposits; gravel enough, however, was seen to justify us in mapping part of it as an old Alluvium.

River Derwent.-The patches of gravel above Yorkshire Bridge are unimportant. The largest, about Derwent Chapel,* shows two terraces (see Horizontal Section of the Geol. Survey, Sheet 69). This and indeed the whole strip of gravel-land makes excellent meadows. From a little below Yorkshire Bridge to Hathersage* is a broader spread of gravel; two or three terraces may be traced in places, but they have been much cut up by later denudation. The lowest of these in the case of a very high flood, say once in 20 years, may be flooded by the river. Between Bamford Mill* and Mytham Bridge* a double terrace may be traced on each side of the river. Lower down the river the alluvial matter is mainly sand which is seen here and there to rest on gravel. Here, however, the flats are liable to be flooded, and the deposit of sand is now going on, being doubtless derived from the waste of the older gravels in the upper part of the stream, which the river itself formed in bygone times, and is now wearing down into finer material.

Caves. Of the great number of caves which are made objects of attraction to visitors to Derbyshire, many are merely old mines, in pipeveins that have communicated with the surface. Others, however, are natural, and, as they are, or have been, intimately connected with the drainage of the country, a few words will be devoted to the principal of them. The famous Peak Cavern at Castleton forms the outlet for the surface-water of the district lying to the west and south-west of this town, the water issuing partly through the cavern, but largely also by a spring at the mouth of the cavern, which is known as Russett Well. The water sinks into the limestone, principally along the boundary of the Yoredale Shale, from Windy Knoll as far at least as Perryfoot, at the fourth milestone west of Castleton. Here a stream from Rushup Edge disappears from view in an open swallow, while the surface-water which was met with in the workings of the Coalpithole Lead Mine was turned into a water-course found in the limestone at 40 fathoms depth, and was seen no more. It may be mentioned that in this watercourse were found deposits of river-gravel, composed of rolled pebbles of Yoredale Shale and Grit, at a point some 400 yards south of the boundary of these rocks. The Giant's Hole, near Peak's Hill, is another large swallow-hole, doubtless communicating with the same system of underground drainage. The water is next seen in the Speedwell Level, in the great cavern in the New Rake, which this level interThe rake ranges a little south of west towards Perryfoot, and the water is seen running to the east. The identification of this under

sects.

* In Map 81 N.E.