Page:Quarterly Journal of the Geological Society of London, vol. 32.djvu/259

Rh 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 :—"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.