CHANGES OF THE EAETh's FLORA AND FAUNA. 47 



certain Immidity, would, if they survived at all, probably 

 undergo visible changes of appearance. While still greater 

 alterations would occur in the plants gradually spreading 

 over the lands newly raised above the sea. The animals 

 and insects living on these modified plants, would them- 

 selves be in some degree modified by change of food, as 

 well as by change of climate ; and the modification would 

 be more marked where, from the dwindling or disappear- 

 ance of one kind of plant, an allied kind was eaten. In the 

 lapse of the many generations arising before the next up- 

 heaval, the sensible or insensible alterations thus produced 

 in each species would become organized — there would be 

 a more or less complete adaptation to the new conditions. 

 The next upheaval would superinduce further organic 

 changes, implying wider divergences from the primary 

 forms ; and so repeated) y. 



But now let it be observed that the revolution thus 

 resulting would not be a substitution of a thousand more 

 or less modified species for the thousand original species ; 

 but in place of the thousand original species there would 

 arise several thousand species, or varieties, or changed 

 forms. Each species being distributed over an area of 

 some extent, and tending continually to colonize the new 

 area exposed, its dififerent members would be subject to 

 different sets of changes. Plants and animals spreading 

 toAvards the equator would not be affected in the same way 

 with others spreading from it. Those sj^reading towards 

 the new shores would undergo changes unlike the changes 

 undergone by those spreading into the mountains. Thus, 

 each original race of organisms, would become the root 

 from which diverged several races differing more or less 

 from it and from each other ; and while some of these 

 might subsequently disappear, probably more than one 

 would survive in the next geologic period : the very disper- 

 sion itself increasing the chances of survival. Not only 



