152 DISTRIBUTION OF EXTINCT ANIMALS. [part ii. 



in mountains of ice around the two poles, would lower the general 

 level of the ocean about 2,000 feet. This would be equivalent 

 to a general elevation of the land to the same amount, and would 

 thus tend to intensify the cold ; and this elevation may enable 

 us to understand the recent discoveries of signs of glacial 

 action at moderate elevations in Central America and Brazil, far 

 within the tropics. At the same time, the weight of ice piled up 

 in the north would cause the land surface to sink there, perhaps 

 unequally, according to the varying nature of the interior crust 

 of the earth ; and since the weight has been removed land would 

 rise again, still somewhat irregularly ; and thus the phenomena 

 of raised beds of arctic shells in temperate latitudes, are ex- 

 plained. 



Now, it is evident, that the phenomena we have been con- 

 sidering — of the recent changes of the mammalian fauna in 

 Europe, North America, South Temperate America, and the 

 highlands of Brazil — are such as might be explained by the most 

 extreme views as to the extent and vastness of the ice-sheet, 

 and especially as to its simultaneous occurrence in the northern 

 and southern hemispheres ; and where two such completely in- 

 dependent sets of facts are found to combine harmoniously, and 

 supplement each other on a particular hypothesis, the evidence 

 in favour of that hypothesis is greatly strengthened. An ob- 

 jection that will occur to zoologists, may here be noticed. If 

 the Glacial epoch extended over so much of the temperate and 

 even parts of the tropical zone, and led to the extinction of so 

 many forms of life even within the tropics, how is it that so 

 much of the purely tropical fauna of South America has main- 

 tained itself, and that there are still such a vast number of 

 forms, both of mammalia, birds, reptiles, and insects, that seem 

 organized for an exclusive existence in tropical forests ? Now 

 Mr. Belt's theory, of the subsidence of the ocean to the extent of 

 about 2,000 feet, supplies an answer to this objection ; for we 

 should thus have a tract of lowland of an average width of 

 some hundreds of miles, added to the whole east coast of Central 

 and South America. This tract would, no doubt, become covered 

 with forests as it was slowly formed, would enjoy a perfectly 



