252 NEOZOIC TIME. [CHAP. XII. 



been British and Belgian forms which, at a subsequent 

 period, when, circumstances permitted, ranged northward 

 and found a lower temperature more congenial. We do 

 not know how many species of the Pliocene mollusca were 

 forced by the increasing cold of the Glacial period to adapt 

 themselves to a cold climate ; some probably would do so, 

 while others were exterminated or driven to more southern 

 climes. Neither does the transportal of the f elstone boulder 

 of Sudbourn, even if accomplished by ice, involve the influx 

 of a current from Arctic regions. 



All these questions will doubtless be ably discussed by 

 Mr. Clement Eeid in the monograph on the British Plio- 

 cene Deposits which he has in preparation, and it would be 

 both premature and presumptuous if I were to attempt a 

 solution of so difficult a problem in the present volume. 

 Before dismissing the subject, however, attention may be 

 called to the opinions formed by Messrs. Kendall and Bell 

 from a study of the St. Erth fossils, with regard to the 

 geographical connections of the sea in which they lived. 

 From the prevalence of Mediterranean species they infer a 

 direct communication with that sea through Normandy 

 and the south-west of France ; while from the absence of 

 Arctic species they are led to think that the Arctic Ocean did 

 not then open into the Atlantic, but that the land commu- 

 nication which is believed to have existed between Europe 

 and North America in Eocene times, by way of Iceland 

 and Greenland (see p. 215), continued to exist through the 

 Miocene and early Pliocene epochs, so as to form a barrier 

 of separation between the Arctic and Atlantic oceans. 



They point out that 1 a submerged ridge, covered by less 

 than 350 fathoms of water, but with deep water on either 

 side of it, extends from Scotland to the Faroe Isles, and 

 has had, as explained by the late Dr. Jeffreys, a great in- 

 fluence in preventing the intermingling of the marine 

 1 '' Qunrt. Journ. Geol. Soc.," vol. xlii. p. 207. 



