THE CHANGE OF CLIMATE. 299 



north, between the coasts of Norway and Greenland. The 

 absence of the Gulf Stream would probably lower the 

 January temperature of Western Europe ten degrees, while 

 the presence of a cold current from the north would make 

 a farther difference of about three or four degrees ;* an 

 alteration of the climate which would apparently be sufficient 

 to account for all the phenomena. This theory, Mr. Hopkins 

 considers as no mere hypothesis, but as necessarily following 

 from the submergence of North America, which has been 

 inferred from evidence of a different nature. 



In this case, of course, the periods of great cold in Europe 

 and in America must have been successive, and not syn- 

 chronous ; and it must also be observed, that in this sug- 

 gested deflection of the Gulf Stream, Mr. Hopkins was 

 contemplating a period anterior to that of the present 

 rivers. For if we are to adopt this solution of the diffi- 

 culty, an immense time would be required. If, when the 

 gravels and loess of the Somme and the Seine were being 

 deposited, the Gulf Stream was passing up what is now the 

 Valley of the Mississippi, then it follows that the formation 

 of the loess in that valley and its delta, an accumulation 

 which Sir C. Lyell has shown to require a period of about 

 100,000 years, would be subsequent to the excavation of the 

 Somme Valley, and to the presence of man in Western 

 Europe. 



Thus, therefore, though the alteration of climate ap- 

 parently indicated by the zoological contents and the physi- 

 cal condition of the beds might, by increasing the power of 

 the floods, add to the erosive action of the river, and by 

 this means diminish, on the one hand, the time required for 

 the excavation of the valley, still the very alteration itself 

 appears, on the other, to require an even greater lapse of time. 



But though the presence of the sandstone blocks, and 

 * Hopkins, I.e. p. 85. 



