THE PLEISTOCENE OR GLACIAL PERIOD. 499 



in detail. The following outline is borrowed essentially from the 

 writings of James Geikie. 1 



The earliest indications of an approaching ice age are met with in 

 the marine deposits of the late Pliocene period. The earlier Pleis- 

 tocene life indicates genial climatic conditions, but toward the close 

 of this initial stage, marine forms adapted to mild temperatures retreated 

 from the North Sea, while boreal types came to occupy their place. 

 Similar migrations affected regions farther south, and many boreal 

 forms found their way into the Mediterranean. On the land, like 

 changes took place, and the luxuriant flora and the great mammals 

 of the Pliocene retreated before the advancing glacial climate. 



During the first glacial epoch, a thoroughly arctic fauna lived in 

 the North Sea, while during the first recognized interglacial epoch 

 following, the arctic fauna retreated from the North Sea. On the 

 land, during this interglacial interval, a temperate flora, comparable 

 to that now existing in England, clothed the British Isles, while the 

 hippopotamus, elephant, deer, and other mammals invaded Britain 

 by way of the land bridge which then connected it with the conti- 

 nent. A similar flora and fauna advanced to corresponding latitudes 

 on the mainland. A luxuriant deciduous flora occupied the valleys 

 of the Alps and flourished at heights which it no longer attains. Toward 

 the close of this interglacial epoch, the temperate flora retired, and an 

 arctic flora gradually took its place. 



During the second glacial epoch, according to Geikie, the ice reached 

 its maximum extent in Europe, and arctic-alpine plants occupied the 

 low grounds of central Europe, while northern mammals, embracing 

 the reindeer, the arctic fox, and the arctic glutton reached the mountain 

 ranges of southern Europe, and even the shores of the Mediterranean. 



During the second interglacial epoch, the arctic-alpine flora and 

 the northern fauna retreated over the lowlands of central Europe, 

 and were replaced by temperate and southern forms. The plants 

 which then occupied northern Germany and central Russia imply a 

 milder climate than the present, and the mammalian fauna, which 

 included the hippopotamus and elephant (Elephas antiquus), was in 

 keeping with the flora. Toward the close of this interglacial epoch, 

 however, a northern facies began to be assumed, and as the third gla- 



1 The Great Ice Age, Third Edition, pp. C07-615. 



