CHAP. XVI.] 
THE BRITISH ISLES. 
819 
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 amphibia. 
Britain „ 18 ,, ,, „ 
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. 
