CHAP. XVI.] 



THE BRITISH ISLES. 



319 



greater part of the life of our country ; and as it certainly 

 occurred during the latter part of the glacial epoch, the sub- 

 sequent 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 per- 

 manent change of climate on the passing away of the glacial 

 conditions appears to have led to the extinction or migration 

 of many species in the adjacent continental areas, where they 

 were succeeded by the assemblage of animals 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 sub- 

 sidence again occurred, cutting off the further influx of purely 

 terrestrial animals, and leaving us without the number of species 

 which our favourable climate and varied surface entitle us to. 



To this cause we must impute our comparative poverty in 

 mammalia and reptiles — more marked in the latter than the 

 former, owing to their lower vital activity and smaller powers 

 of dispersal. Germany, for example, possesses nearly ninety 

 species of land mammalia, and even Scandinavia about sixty, 

 while Britain has only forty, and Ireland only twenty-two. 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. This poverty attains its maximum in the 

 reptiles, as shown by the following figures : — 



Belgium has 22 species of reptiles and ampliibia. 

 Britain „ IH 



Ireland 4 „ „ 



Where the power of flight existed, and thus the period of 

 migration was prolonged, the difference is less marked ; so that 

 Ireland has seven bats to twelve in Britain, and about 110 as 

 against 130 land-birds. 



