EXCURSIONS OF AN EVOLUTIONIST 



that in the early Tertiary times the antarctic land 

 was much more extensive than at present. Now 

 an elevation in the antarctic region, increasing 

 the deposit of snow and ice about the south 

 pole, and thus increasing the difference of tem- 

 perature between the south pole and the equator, 

 would be just what was needed to convert the 

 fickle monsoons of the Indian Ocean into a 

 steady and powerful trade-wind, that would 

 drive the warm water northward through the 

 channel between Europe and Asia, even as far 

 as the north pole. This current from the Indian 

 Ocean must have been more than equal to the 

 Gulf Stream in heating power, and its effect 

 would be to prevent any accumulation of ice 

 within the Arctic Circle, and to produce in 

 Greenland such a climate as it is known to have 

 enjoyed in the Miocene period, when it was 

 covered with a vegetation as luxuriant as that 

 of Virginia at the present day. 



This question is discussed at considerable 

 length and with great ability by Mr. Wallace, 

 in his treatise on " Island Life." His argument 

 is in some respects the most valuable contribu- 

 tion that has ever been made to our understand- 

 ing of past climatic changes. He makes it per- 

 fectly clear that while Mr. Croll's astronomical 

 interpretation of the Glacial period is perfectly 

 correct in principle, nevertheless extensive gla- 

 ciation cannot take place unless the geographi- 



