48 THE MIGRATIOX OF BRITISH BIRDS 



Belgium, and Germany, about as far as E. long. lo , 

 together with that greater portion of France which re- 

 mained free from permanent glaciers and snow-fields. 

 Thanks to the researches of geologists and paLxonto- 

 logists we can form a pretty good general idea of the 

 state of this area during the Glacial Epoch. At the 

 climax of the Ice Age, and probably for ages after that 

 event, there can be little or no doubt whatever that 

 bird-life was utterly exterminated from all parts of 

 Western Europe, including the British Islands, say north 

 of lat. 52". The present area may be described as the 

 head-quarters of those now high Arctic species that 

 in those remote days contrived to live and thrive 

 and perhaps become modified into " boreal " forms 

 amidst the rigours of the glacial ages, practically on 

 the margins of the snow-fields and ice-sheets. The flora 

 of this region was very similar to that which charac- 

 terizes Scandinavia and the high Alps at the present 

 time, perhaps the most characteristic Arctic plants of 

 Southern England then being equally modified mosses, 

 lichens, saxifrages, and the dwarf birches, and willows 

 of various species, as were, for instance, ascertained 

 by the late Mr. Pengelly and Professor Heer, and again 

 by Mr. Nathorst, to occur in the clays of Devonshire. 

 The reindeer and the elk, the lemming, the glutton, the 

 Arctic fox and the pika — all now thoroughly Arctic 

 species — were dwellers in this area, as their remains 

 have so eloquently demonstrated, and with a range base 

 in that area which must have endured from Pre-Glacial 

 times, or a dispersal thereto from more eastern and 

 southern non-glaciated areas during the continuance of 

 glacial conditions elsewhere {co)if. Map, p. 47). 



