264 PROGRESS OF SCIENCE IN THE CENTURY. 



over a thousand feet above sea-level; the remains of 

 boreal animals in North Temperate countries, and 

 so on, corroborate the main conclusion. 



In what are called Pleistocene times enormous 

 contineutal mers de glace covered immense areas in 

 Europe and North America. Great snow-fields and 

 local glaciers accumulated especially in those areas 

 where the precipitation of snow and rain is now 

 most abundant, and where in some cases, as in 

 Norway and the Alps, there are still relics of the 

 olden times. North of Central Germany and Central 

 Russia all Europe was buried in ice; the whole of 

 North America north of a line between New York 

 and the Rockies was glaciated. The mean annual 

 temperature of Central Europe must have been low- 

 ered many degrees (perhaps 10° or 11° F. according 

 to Penck, 5J°~7° E. according to Briickner). The 

 climate of Southern Germany then would be like 

 that of Northern Norway now, and so on; in short, 

 "in glacial times a wholesale displacement of cli- 

 matic zones took place.'' * 



It is some progress, then, toAvards a clearer inter- 

 pretation of the earth, that what were by older 

 geologists regarded as the results of Noah's flood 

 are now known to be the marks of a Great Ice Age — 

 which, though very gradual in its coming and going, 

 wrought great changes upon the face of nature and 

 on the distribution of plants and animals. 



But as the study of glacial phenomena has be- 

 come more extensive and more careful, the inter- 

 pretation has become more complex. Thus, the 

 discovery of " interglacial deposits," whose fossils 

 indicate conditions of warmth — often greater than 



* Prof. James Geikie. Trans. Victoria Inst.y xxvi., 1892- 

 93, p. 222. 



