8 LLOYD'S NATURAL HISTORY. 



epoch, the subsequent elevation and union with the Continent 

 cannot have been of very long duration, and this fact must have 

 had an important bearing on the character of the existing 

 fauna and flora of Britain. We know that just before and 

 during the Glacial period we possessed a fauna almost, or quite, 

 identical with that of adjacent parts of the Continent and 

 equally rich in species. The submergence destroyed this 

 fauna ; and the permanent change of climate on the passing 

 away of the Glacial conditions appears to have led to the ex- 

 tinction or migration of many species in the adjacent continen- 

 tal areas, where they were succeeded by the assemblage of ani- 

 mals now occupying Central Europe. When England became 

 continental, these entered our country; but sufficient time 

 does not seem to have elapsed for the migration to have been 

 completed before subsidence again occurred, cutting off the 

 further influx of purely terrestrial animals, and leaving us with- 

 out the number of species which our favourable climate and 



varied surface entitle us to The depth of the 



Irish Sea being somewhat greater than that of the German 

 Ocean, the connecting land would there probably be of small 

 extent and of less duration, thus offering an additional barrier 

 to migration, whence has arisen the comparative zoological 

 poverty of Ireland." 



It will be apparent from this that Dr. Wallace attributes the 

 clean sweep, which he considers to have been made of the an- 

 cient British fauna, not to the ice-sheet at the epoch of maxi- 

 mum glaciation, but to a submergence of much later date. 

 It does not appear, however, that the evidence that the sub- 

 mergence in question took place at such a late date is by any 

 means decisive; and other geologists attribute the disappear- 

 ance of the greater part of the fauna to the ice-sheet itself, a 

 view with which we ourselves are more inclined to agree. On 

 the other hand, as we shall presently see, another writer disputes 



