2CO HEREDITY AND EVOLUTION IN PLANTS 



12. Denudation of the Land Surface. — In the course of 

 ages even lofty mountains are planed down by erosion, 

 and the arctic and sub-arctic species of the high altitudes 

 thus undergo extinction. Furthermore, erosion may be 

 coupled with general subsidence. In fact, not only do 

 geologists now recognize numerous old mountain "roots," 

 such for example as the Adirondack region of New York 

 State, but there are also abundant evidences of periodic 

 emergencies and subsidence of areas of continental extent, 

 quite throughout geologic time. The climatic and other 

 environmental disturbances accompanying such changes 

 would inevitably result in the extinction of certain species. 

 (See also If 129.) 



