8 THE MIGRATION OF BRITISH BIRDS 



recent search has shown that in the other localities where 

 marine shells have been found in drift at great elevations 

 similar foreign rocks occur, rendering it almost certain 

 that the same ice-sheets which have distributed foreign 

 erratics so Avidely over our country, and which in doing 

 so Diust have passed over the sea-bottom, have in a few 

 cases carried with them a portion of that sea-bottom and 

 deposited it with the erratics in the places where both 

 are now found." If the drift be taken as evidence of 

 submergence, then, as Mr. P. F. Kendal pointedly 

 remarks {Man and the Glacial Period, p. 178) : "A sub- 

 sidence of the Yorkshire Wolds took place on the east, 

 but not in the centre or west ; that the Pennine Chain 

 was submerged on the western side to a depth of 1400 

 feet, and on the east to not more than 30x3 feet, even on 

 opposite sides of the same individual hill ; that all the 

 lowlands between, say, Bacup and the Welsh border, 

 were submerged, and that the hills near Frondeg par- 

 took of this movement, but only on their eastern sides ; 

 that the centre of Wales was exempt, but the summit 

 of Moel Tryfaen forms an isolated spot submerged, while 

 the surrounding country escaped. These absurdities 

 might be indefinitely multiplied, and they must follow 

 unless it be admitted that the phenomena are the results 

 of glacial ice, and that the ice can move uphill." That 

 the latter circumstance is a fact I need scarcely say has 

 been proved by irrefutable evidence. It is also very 

 • nteresting and suggestive to remark how the supporters 

 of the " great submergence " hypothesis assert that the 

 subsidence dwindled down to zero in the southern por- 

 tions of England, say to a line drawn between Bristol 

 and London, curving northward as far as Warwick, 



