302 



HISTORICAL GEOLOGY 



Rockies are so tilted that they are 3000 feet higher close to the 

 mountains than they are farther east. Also the fact that many 



Fig. 184 

 Map showing the surface distribution (areas of outcrops) of Tertiary and later 

 volcanic rocks in North America. (Modified by W. J. M. after Willis, 

 U. S. Geological Survey.) 



large areas of Tertiary deposits now lie from 5000 to even 10,000 

 feet above sea-level, pretty clearly indicate notable elevation since 

 their deposition, because such deposits must have been formed in 



