PAST GEOGRAPHICAL MUTATIONS 7 



probable appearance of Western Europe during at any 

 rate the closing period of Pleistocene and early Post- 

 Glacial time. That a large portion of the British Islands 

 has been submerged to a depth of about 1400 feet 

 during the Glacial Epoch has long been the almost 

 universal opinion of geologists ; the chief, if not only 

 evidence of this great submergence being the occurrence 

 in a few localities of glacial gravels and drifts containing 

 marine shells. Strong evidence against this " great 

 submergence," however, is to be found in the fact that 

 the shells in these drifts differ considerably in habit, 

 some belonging to sandy, others to muddy bottoms, 

 some only known to exist below tidal water, others 

 confined to the shore, consequently they could not well 

 have lived together in the places where their for the 

 most part fragmentary remains are now found. Again, 

 no evidence of this submergence is to be met with on 

 the English lowlands, which, if it had really occurred, 

 would have formed the bottom of a sea no less than 

 1200 feet in depth, and must have left traces of old 

 beaches or marine remains characteristic of such a vast 

 depression. As Dr. Wallace recently remarked {Fort- 

 nightly Reviezu, Nov. 1893, p. 633) : " In consequence of 

 these various difficulties it was suggested by the late Mr. 

 Belt that the great Irish Sea ice-sheet had carried up a 

 portion of the sea-bottom embedded in its substance, 

 perhaps containing deposits of shells of various periods, 

 and thus explaining the intermixture of species as well 

 as their fragmentary condition. The fact that boulders 

 and pebbles from Scotland, Ailsa Craig, and Cumber- 

 land have been found in the Moel Tryfaen beds almost 

 amounts to a proof that they were so uplifted ; and a 



