SUMMARY AXD COXCLUSION 2S7 



with such dispersal. We have shown that the gradual 

 severance of the British Islands from continental land is 

 also quite in accord with the present distribution of 

 birds over their area ; whilst the necessity of a former 

 much greater land extension between Greenland and 

 Europe is shown to be imperative. 



We next pass to a consideration of the Glacial Epoch, 

 and its results upon the fauna and flora of the regions 

 affected. By the aid of a new Law of Dispersal, I have 

 endeavoured to show that the effects of this Glacial 

 Epoch must have been very different from those which 

 biologists have universally accepted and described. I 

 have shown that the conditions of the Ice Age, instead 

 of being grand incentives to Southern Emigration, 

 exerted a vast exterminating influence, and that they 

 must have caused the utter extinction of every species 

 whose breeding range was entirely confined to the areas 

 glaciated, or sufficiently within the influence of glaciation 

 to render existence impossible. The effects of the Glacial 

 Epoch on the dominant Euro-Asian fauna are shown to 

 be exterminating rather than incentive to Southern Emi- 

 gration. The only species that survived were those that 

 occupied a southern and continuous range base during 

 Pre-Glacial time. These southern Range Bases (or what 

 are perhaps better described as Refuge Areas), so far as 

 British birds are concerned, are then defined. I then 

 proceed to show that the breeding range of all surviving 

 species must have extended at least as far south as these 

 limits during Pre-Glacial time, and that the Glacial 

 Epoch exterminated the northern portions of such 

 species, or contracted the range of such as were migra- 

 tory, the habit of migration not being acquired during 



