THE GLACIAL RANGE CONTRACTION, ETC. 63 



extermination of birds in the Arctic and North Tem- 

 perate regions ; the passing away of that ungenial 

 cHmate marked the commencement of their return — 

 the beginning of that vast movement northwards of 

 birds which even at the present day has not ceased, 

 as will be seen in a future chapter,^ These vast 

 changes of climate, there is every reason to believe, 

 took place almost imperceptibly during the course 

 of ages. As the cold climate came on which was 

 eventually to culminate in the third glacial period, the 

 range of the temperate fauna and flora was gradually 

 contracted south by extermination, and that of the 

 "Arctic" fauna and flora slowly followed. Each re- 

 curring winter waxed colder and colder, possibly so 

 slowly that no single generation of species detected 

 the change or were perceptibly influenced by it, yet 

 gradually the temperate range of birds became less and 



1 Before the Glacial Epoch finally passed away several severe 

 fluctuations of climate occurred, cuhiiinating in one more Glacial 

 Period (the fourth), designated by Professor Geikie as the epoch 

 of the Great Baltic Glacier, During this period Iceland, most of 

 North Scotland, and the highest mountains of England, Wales, 

 and Ireland, together with nearly the whole of Scandinavia and 

 Finland, the Alps, and parts of the Caucasus and the Pyrenees, 

 were glaciated. All living things within glacial influence must 

 have perished during this era, but the extermination was on 

 nothing near so vast a scale as that which characterized the 

 glacical periods preceding it. That this fourth glacial period was 

 a severe check to the emigration of species in certain directions 

 is unquestionable, and its influence in such range extension con- 

 tinues to be demonstrated by the distribution of birds in Western 

 Europe, as we shall eventually learn. The student must bear in 

 mind that the later and less intense periods of the Glacial Epoch 

 successively affected smaller and smaller areas of country — a fact 

 of little or no consequence so far as concerns our general argument, 

 but of importance in studying the present geographical distribution 

 of species. 



