Luring Post-Miocene Times. 19 



But there is another of the sciences which we can call in 

 to aid us in fathoming the problem. 



If we turn to the natural history of this hemisphere, we 

 find that the present geographical distribution of plants and 

 animals absolutely requires a glacial period to account for 

 its anomalies. 



Darwin is emphatic enough on this point. He tells us 

 that " we must bear in mind the occurrence in both hemi- 

 spheres of former glacial periods, for these will account for 

 the many quite distinct species inhabiting the same widely 

 separated areas, and belonging to genera not now found in 

 the intermediate torrid zone. ... In the regular course 

 of events, the Southern Hemisphere would in its turn be 

 subjected to a severe glacial period, . . . and then the 

 southern temperate forms would invade the equatorial low- 

 lands. The northern forms which had then been left on the 

 mountains would now descend and mingle with the southern 

 forms. Thus we would have some few species identically 

 the same in the northern and southern temperate zones, and 

 on the mountains of the intermediate tropical regions" (Or. 

 Species, eh. XII., pp. 339, 340). 



When we seek confirmation of these views of Darwin's, 

 we find it. Baron von Mueller reports the discovery of 

 European species of plants upon our mountains, and Dr. 

 Hooker points out that certain peculiarly Australian forms 

 of vegetation now live upon the heights of Malacca, India, 

 and Japan. Further, there are northern forms of fish and 

 seaweed living upon our coasts, although absent from the 

 seas which intervene between Australia and the habitat of 

 the other members of these families. 



No naturalist has given more consideration than has 

 Wallace to the distribution of the flora and fauna of this 

 quarter of the globe, and his statements are entitled to 

 attention. If we compare the distribution of our plants, as 

 he describes its occurrence, with the plan of distribution 

 which we should expect to succeed to a glacial and sub- 

 merged period, we must be struck with the remarkable 

 degree of accord which they present. 



If our climate be recovering from a glacial period, as we 

 believe that it is, then all the temperate zones will be 

 moving northward toward the equator, the warmer ones in 

 front, the colder ranked behind. As this occurs the flora 

 and fauna follow them, keeping slightly in the rear ; for 

 each temperature as it withdraws from a district has to pull 



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