550 



CENOZOIC ERA— AGE OF MAMMALS. 



ing, scoring, etc., of the rock show that the agent of the shifting has 

 been ice. 



Extent. — The general extent of these more conspicuous and char- 

 acteristic phenomena, viz., the glaciation, the stony clay, and the great 

 boivlders, is down to about 40° north latitude. The line of southern 

 limit cuts the Atlantic coast about 40°, near New York ; it then bends 

 a little southward to 37° 30' in Southern Illinois, and then turns a little 

 northward again as it passes west, and may be traced northwestward 

 nearly to Montana (Fig. 931), and reappears on the Pacific slope in the 



Fig. 930.— Moraines of Grape Creek, Sangre del Cristo Mountains, Colorado (after Stevenson). 



southern portion of British Columbia (Dawson). Beyond this the 

 characteristic phenomena mentioned above are not found, but in the 

 valley of the Mississippi, and on each side to a considerable distance, 

 a superficial gravel and pebble deposit, containing northern bowlders — 

 called by Prof. Hilgard " Orange Sand " — extends to the shores of the 

 Gulf. Evidences of local glaciers in the form of moraines are found 

 abundantly in the Colorado Mountains (Fig. 930). 



Marine Deposits, — Along the Atlantic coasts we find no marine 

 deposits of this time, for the obvious reason that the continent was then 

 more elevated than now ; whatever marine deposits were then formed 

 are now covered by the sea. 



