CHAPTEK IX. 
THE AGE OF GREAT MAMMALS. 
What may we expect now ? We Lave seen the 
reign of fire and water. Then life, at first rather low 
in structure and simple in wants, began its struggle 
for existence in the seas. Xext the great fishes came 
to usurp authority in the waters. They were back¬ 
boned animals requiring higher conditions for a liv¬ 
ing and better equipment for defense. During the 
coal-forming period interest is transferred to the land. 
Great trees and broad-leaved plants take up every 
foot of the moist soil. Then life makes another leap 
toward higher conditions when large lizards come 
forth from the waters, taking on powers suited to 
terrestrial existence. Air, land, and water have grad¬ 
ually become fitted for lung-breathing creatures. 
May we not expect man, the head of creation ? Let 
us examine the fossil pages of this chapter. 
The waters continued their work of denudation, 
cutting narrow gulches in some places and broader 
depressions at others, so that when parts of the crust 
again became sea-bottom, the newly formed rocks 
filled the cuts, thus showdng clearly the break in the 
rock system. 
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