The Scottish Naturalist. 



3i5 



pursuers, with much loss, whole species and even genera being 

 extinguished in the process, others being modified, and consid- 

 erable alteration taking place in the geographical distribution of 

 almost all — truly affording a fine illustration of the phrase, "sur- 

 vival of the fittest." In some cases, as we have seen, only the 

 fragments remain on two or three favoured spots on the moun- 

 tains where the lithological character of the soil seems to prevent 

 their extension to the regions beyond. And this last may per- 

 haps furnish the key to some of the recondite causes why so 

 many of our Highland hills are so poor in alpine species. 



Mr A. R. Wallace, in ' Island Life,' gives as a reason why 

 Britain is poor in species of both fauna and flora, that "there is 

 good evidence that a considerable portion, if not the entire area, 

 of our country has been submerged to the extent of upwards of 

 1300 feet, shell-bearing gravels having been found at that height 

 on some of the hills, so that only the hills would remain as 

 groups of rocky islets. This submersion must have destroyed 

 the 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 im- 

 portant bearing on the character of the existing fauna and flora 

 of Britain. 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, and leaving us 

 without the number of species which our favourable climate and 

 varied surface entitle us to." 



We have seen how very meagre the alpine flora of Ireland is, 

 only numbering about 25 species : but that is not all. The 

 whole Irish flora does not number more than, if as many species 

 as, are contained in the single comparatively small county of 

 Forfar. The same anomaly is presented by its fauna. How is 

 this to be accounted for? Is it that the climate is less denial 

 than that of England or Scotland, or the soil less productive? 

 That the contrary is the case is well known. The following 

 geological and physical changes will account for it, and the ex- 

 planation may also help to illustrate the cause of the apparent 

 freaks and irregularities of distribution in our own country. 



At the close of the glacial era Britain was receiving its flora 

 from Europe. This flora was gradually finding its way west- 

 ward. Ireland would thus be the last to receive her flora, which 



