148 INTRODUCTION. 



ought to be found to have made nearly an equal advance, 

 and to be pretty equally dispersed over the earth, for we 

 know of nothing in their organization that should give 

 any considerable advantage in this respect to one over 

 another. The species of the two hemispheres should 

 also be in general the same. If all the species then, 

 originated on the eastern continent, how has ,it happened 

 that those that have reached the western continent, have 

 ill general, left none of their kind behind them ; or that 

 peculiar species exist in small islands or groups of islands 

 far removed from other land ? If it be said that in the 

 long lapse of ages, species once universally diffused have 

 become extinct in particular regions, and that the sur- 

 vivors are confined to more limited ranges, we ask how 

 it happens that the testaceous remains discovered by 

 geological research, differ as much from existing species 

 as the recent species of the two contments differ from 

 each other. It seems to us that the facts taken for 

 granted in these objections are inconsistent with any 

 other theory than that of different foci of creation, and 

 that this theory is sustained by all that we know of the 

 geological revolutions of the earth, and of the condition 

 of the species formerly existmg upon it. 



Having thus adopted the theory of distinct zoological 

 centres, and admitting that as successive portions of the 

 earth's surface emerged from the waters, and became 

 adapted to sustain the different classes of animals, those 

 races which were fitted for the then existing physical 

 condition of things, were brought into being by the pro- 



