EXCURSIONS OF AN EVOLUTIONIST 



extraordinary. Hitherto, during the Tertiary 

 period, the temperature of Europe seems to have 

 been steadily but slowly decreasing, from the 

 Eocene epoch, when it was sub-tropical, to the 

 end of the Pliocene, when it was temperate, 

 though warmer than at present. But in the 

 Pleistocene epoch there were at least four 

 or five, and probably several more, extreme 

 changes from a warm to a cold climate, and 

 back again. This period, or the greater part of 

 it, has been known as the " Glacial Epoch " or 

 the " Great Ice Age ; " but recent researches 

 have shown that over Britain and central Europe 

 there were several glacial epochs, alternating 

 with warm inter-glacial periods of long duration. 

 When the cold was at its maximum, the whole 

 area of Finland, Scandinavia, and Scotland, with 

 the North and Baltic seas, was buried under a 

 stupendous sheet of ice, varying from 1000 to 

 2000 feet in thickness ; and this ice-sheet sent 

 off glaciers as far east as Moscow, and as far 

 south as Dresden, while the Alps, the Pyrenees, 

 and the mountains of Auvergne became centres 

 of glaciation, inferior, indeed, to the great north- 

 ern ice-sheet, but still immense in extent. While 

 the climate of Pleistocene Europe thus came to 

 be similar to that of modern Greenland, parallel 

 phenomena were occurring all over the northern 

 hemisphere. The continent of North America 

 was deeply swathed in ice as far south as the 

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