298 



ASTRONOMICAL AND GEOGRAPHICAL CAUSES [Ch. XIII. 



10° farther south, on the west side of the Atlantic than on 

 the east side. This difference, as before pointed out, p. 236, is 

 dependent on purely geographical and not on astronomical 

 causes — the direction of the Gulf-stream from south-west to 

 north-east — the cold polar current flowing south along the 



America — the extension of the land of the 



North 



latter continent continuously towards the pole in the same 

 latitudes as those where there is open sea to the north of 

 Europe, are sufficient to explain the present course of the 

 isothermals ; and if the cold w r ere now augmented by the 



>m 



the isothermals alluded 



same 



farther south because the new refrigerating influence would 

 operate equally on the eastern and western hemisphere. If 

 the effect would not be exactly equal on both sides of the 

 Atlantic, it would be in favour of greater curves in the 

 direction in which thev now bend, because the 



increase 



snow and ice would be greatest on the side where there is 



most 







Now 



tion, such as erratic blocks, scored surfaces of rock, striated 

 boulders, and deposits filled with arctic species of marine 

 shells, are to be seen in full force on the North American 

 continent ten or more degrees farther south than in Europe. 

 If we could assume, therefore, that geographical conditions 



had been 



would be in favour 



our attributing the greater intensity of cold in the Glacial 

 Period to a maximum excentricity. Our full reliance, how- 

 ever, on this line of reasoning is somewhat weakened when 

 we reflect that a moderate amount of geographical change 

 in a very high latitude — such as the addition of some islands 

 near the pole, or the increased height of some of the land now 

 existing between latitudes 70° and 80° N.— 

 the cold both of the eastern and western hemispheres, acting 



inig 



&t» 



North 



know 



as a positive fact, that geographical changes have taken place 



commencemen 



f. 



of the Glacial Period, although we cannot affirm that when 

 the cold was at its height there was a greater proportion of 



