294 



GENERAL ZOOLOGY 



volcanic upheavals must have been frequent as fire and water 

 struggled for the mastery. During this time, of course, no 

 life was possible. As the crust continued to cool it was 

 upheaved and formed land. When the waters had cooled 

 sufficiently to permit of it, life appeared, but in what form 



FIG. 146. North America in the Archsean Era 

 (From Dana's Manual of Geology) 



we do not know. It is thought that this early life may have 

 been plant rather than animal in its nature, since plants 

 to-day, with the exception of the fungi (mushrooms, bacteria, 

 etc.), feed upon mineral matter, while animals require plant 

 or animal food. As regards the temperature at which life 

 became possible, it is known that plants live now in the hot 

 springs of the West in water reaching 180 F. 



