382 Geology of 



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 the land would rise again, still 

 somewhat irregularly ; and thus the phenomena of raised beds of 

 arctic shells in temperate latitudes are explained." 



"Xowit is evident, that the phenomena we have been considering — • 

 of the recent changes of the mammalian fauna in Europe, Xorth 

 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 simul- 

 taneous occurrence in the Northern and Southern Hemispheres, and 

 where two such completely independent sets of facts are found to 

 combine harmoniously, and supplement each other on a particular- 

 hypothesis, the evidence in favour of the hypothesis is greatly 

 strengthened. An objection 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 maintained itself, and 

 that there are still such a vast number of forms, both of mammalia, 

 birds, reptiles, and insects, that seem organised for an exclusive 

 existence in tropical forests ? Now, Mr. Belt's theory of the subsi- 

 dence 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 tropical climate, and would thus afford ample area for the 

 continued existence and development of the typical South American 

 fauna, even had glaciers descended in places so low as what is now the- 

 level of the sea, which, however, there is no reason to believe they 

 ever did. It is probable, too, that this low tract, which all round the 

 Gulf of Mexico would be of considerable width, offered that passage 

 for intermigration between Xorth and South America, which led to 

 the sudden appearance, in the former country in post-pliocene times, 

 of the huge megatheroids from the latter — a migration which took 

 place in opposite directions, as we shall presently show." 



AVithout giving altogether my assent to such theory, it nevertheless 

 will be of some use to apply it to ^ T ew Zealand, and to see what the 

 effects of the lowering of the sea level for 2000 feet would have been. 



