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 tothe 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 anyexclusive 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 
