20 THE MIGRATION OF BRITISH BIRDS 



elephants, rhinoceroses, and hippopotamuses, horses, 

 oxen and deer, hares and rabbits, wolves, foxes, lions, 

 and hyaenas joint occupants of the same, regions." The 

 geographical conditions at this period were such that 

 the coast-line of North-western Europe extended beyond 

 the British Islands, reaching what we have seen was 

 probably the lOO-fathom contour, and in the INIcditer- 

 ranean region the land was distributed differenth' from 

 what is now the case. 



Once more a change of climate and of physical con- 

 ditions are initiated by the coming on of another — the 

 third — glacial period, and another great extermination 

 of the fauna and flora is commenced. As the cold 

 increased the southern forms vanished from northern 

 areas, and as the rigours of the climate became more 

 intensified, temperate and boreal forms became less 

 northerly in their distribution, until ultimately the dwarf 

 birch, the Polar willow, and Arctic mosses, saxifrages, and 

 lichens inhabited the lowlands of Central and Southern 

 Europe ; the mammoth and the glutton, the reindeer, 

 the marmot, and the musk sheep dwelt only upon the 

 northern shores of the Mediterranean. During this era 

 the sea is presumed to have invaded the plains of the 

 English Channel and the German Ocean, whilst it is 

 suggested that the low grounds of Prussia were sub- 

 merged. The British area, with the exception of England 

 from Yorkshire southwards, was for the most part 

 covered with snow-fields and ice, and the surrounding 

 seas were filled with glaciers ; many of the mountain 

 regions of Central hAU'opc were glaciated ; and even 

 as far south as Gibraltar and Malta heavy snows 

 and severe frosts prevailed. Again the severity of 



