1872.] DAKXNS YOEKSHIKE GLACIAL PHENOMENA. 383 



this line of hills is broken through by the vallejs of the Wye, in 

 Derbyshire, and of the Calder and the Aire, in Yorkshire. 



In Derbyshire and the part of Yorkshire south of the Aire basin, 

 no glacial drift has been found on the eastern slope of the chain, save 

 where the latter is broken through by the above-named valleys. Thus 

 in Derbyshire plenty of drift occurs in the valley of the Wye and in 

 that of the Derwent below its junction with the Wye, as if some of 

 the drift that is so plentiful on the western slope of the Pennine 

 chain had come eastward through the Wye valley ; but north of the 

 Wye none is found in Derbyshire on the eastern slope of the chain. 

 Again, some boulders of transported rocks, granite, and other 

 foreigners are said to have been found in the bed of the Calder ; but 

 no drift-deposits have been found in the Calder basin east of the an- 

 ticlinal axis, save one patch of Boulder-clay at Mixenden, some miles 

 above Halifax, quite at the edge of the driftless area. The boulders 

 above mentioned vpould seem to have been washed out of the drift of 

 Lancashire. On the other hand, the western slope of the Pennine range 

 is everywhere thickly covered with drift nearly up to the level of the 

 watershed. But when we cross the Oxenhope moors, from the basin 

 of the Calder into that of the Aire, the state of things is very 

 diiFerent. The basin of the Aire and the whole country northward 

 is thickly covered with drift indifferently on the east and west. 



The drift of Lancashire and Cheshire is considered to be marine, 

 for the following reasons : in the first place, it contains far- 

 transported rocks, such as granite ; in the second place, it is pro- 

 longed through the Wye valley, while nowhere else is drift found on 

 the eastern hills, thus showing it had floated through the gap. 



I will now describe certain general phenomena in connexion with 

 the drift of the Aire basin and the country northward, from which it 

 will appear, I think, that the mass of it is due to land-ice. 



In the first place, this drift contains no foreigners — that is, no 

 stones that may not have come from the rocks of the basin where it is 

 found. Thus in the basin of the Aire, east of Skipton, the stones 

 are entirely Carboniferous grits, sandstones, and limestones, all 

 which rocks occur in the basin of the Aire ; while north of Skipton, 

 on the edge of the great plain that stretches to the Pibble, a few 

 small, much-worn Silurian pebbles are occasionally found, which 

 have doubtless come from the Silurians of Pibblesdale. 



Again, in Wharfedale we have nothing but Carboniferous rocks in 

 the drift, with one exception : this is near Threshfield, where Silurian 

 erratics do occur ; but they are special to that locality, and are found 

 AA'here the valley, ceasing to be a narrow dale, opens out into a plain 

 reaching as far as the Kibble. In the high dale the drift is entirely 

 composed of local rocks. 



It would seem, then, that whatever brought the drift was some 

 agent acting locally. It was not, then, either ice floating from afar or 

 necessarily a universal ice-sheet overriding the watersheds, though I 

 shall presently give reasons for thinking there was such an ice-sheet. 



Further, in Wharfedale and its affluents, in Wensleydale (as far 

 as I know) and its affluents, the following phenomena are universal. 



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