298 NEOZOIC TIME. [CHAP. XIII. 



and that by this subsidence Ireland was first of all separated 

 from England, and then a little later on England was 

 severed from the Continent. This gradual severance before 

 the complete establishment of the European fauna in our 

 islands seems to be indicated by the peculiar distribution 

 of species, and especially of the mammals and reptiles, at 

 the present time. This was first pointed out by Professor 

 E. Forbes, and has been more fully investigated by Mr. 

 A. E. Wallace, 1 who gives the following figures : 



Germany has 90 species of Mammalia. 



Britain ,,40 



Ireland 22 



Belgium has 22 species of Eeptilia and Amphibia. 



Britain 13 ,, 



Ireland 4 



We must suppose, therefore, that the land did not 

 remain very long at the elevation shown in Plate XIV., 

 and that the connection between England and Ireland 

 was soon reduced to the condition of an isthmus, which 

 was submerged before more than four out of the twenty- 

 two continental species of reptiles had crossed in sufficient 

 numbers to effect a permanent settlement in Ireland. 

 Measured in number of years the time taken to effect 

 this may have been long, but geologically speaking it 

 was short. Ireland then became an island, while England 

 still remained a part of the Continent, and there was 

 doubtless a time when the line of 40 fathoms formed the 

 coast-line of Britain, and when the geography was such 

 as is represented in Plate XV., which shows the area that 

 would be converted into land by an upheaval of 40 fathoms 

 (240 feet) at the present time. 



The coincidence of the coast-line with the 40-fathom 

 line was, however, only an epoch in the history of the 

 1 " Island Life," p. 319 et scq. 



