ON OPPOSITE SIDES OF THE PENNINE CHAIN. 187 



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 * : — 

 " Prom what I can see, there is nothing whatever in this deposit 

 to separate it from the superficial deposits in the valley near Cas- 

 tleton, which you will find pretty well everywhere. When I ex- 

 amined 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 neigh- 

 bourhood." These examples will, I trust, suffice to show that over 

 this large area, extending from Skipton in the north, by Tod- 

 morden, to Castleton in the south, a general absence of drift de- 

 posits 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 sup- 

 posing 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 con- 

 sideration 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 pheno- 

 menon 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. 



* Trans. Manchester Geological Society, vol. xiii. p. 124. 



