194 



GLACIAL EPOCH. 



[Ch. X. 



,11111 S 



an arctic character in tlie drift of England, Trance, and 

 Germany.*" Some zoologists conjectnre that the fossil species 



was fitted for a cold climate, but it seems 

 more probable that when the temperature of the river water 

 was congenial to the Cyrena above mentioned, it was also 

 suited to the hippopotamus. 



Glacial Epoch. — The next step of our retrospect carries us 

 back to what has been called the Glacial Epoch, which, 

 though for the most part anterior to the valley-drifts and 

 cave deposits of the paleolithic age above 

 still so closely connected with that period that we cannot 

 easily draw a line of demarcation between them. Thedisper- 



mentioned 



sion of large angular fragments of rock, called erratics, ovei 

 the northern parts 



America 



om 



.fficult 



before it began to be suspected that they might have been 

 transported by ice, and at a period when large parts of the 

 present continents were submerged beneath the sea. 



These blocks are observed to extend in Europe as far south 



Amer 



marked that some 



one or more of their sides in a manner strictly analogous to 



moraines 



in the Alps. In many areas covered with them both m 

 America and Europe, the underlying solid rocks were seen 

 to be marked by similar scratches and rectilinear furrows, 

 their direction usually coinciding with the course which the 

 erratics themselves had taken. As both the smoothing and 

 striation of the transported fragments and the surfaces of 

 the rocks in situ were identical in character with effects 

 recently produced by existing glaciers, it was at length ad- 

 mitted, but not till after the point had been controverted for 

 a quarter of a century, and in direct opposition to the opinion 

 of the earlier geologists, that the climate which preceded tiie 

 historical was not only colder as far south as lat. 50 in 



* The jaw-bone of a monkey {Ma- now considered as of very donbtfu 

 cacus plioccnus, Owen), which I formerly authenticity, 

 cited as belorging to the Essex drift, is 





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