ROCKY MOUNTAIN BASIN 

 DEPOSITS 



GREAT PLAINS 

 DEPOSITS 



ZONES 

 (jlyfjtoOicriuni 



FORT UNION INTRODUCTION OF ANCESTORS 



(MONT.) 



2'^Faunal Period 



ARCHAIC MAMMALS 

 ONLY 



1^* Faunal Period 



Cojyphodon 

 and, 



MAMMALS 



Pantolam hda 

 Polymastodon 



CRETACEOUS 



_I_J 



CLOSE OF THE AGE OF REPTILES 



EXTINCTION OF DINOSAURS 



By permission of the U. S. Ceologlcal Survey. 

 Fig. 10. — Successive and overlapping Formations of the Rocky Mountain Region in 

 Eocene and Oligocenc times. Key to the series of scale sections in the subsequent pages ; all 

 the sections ur(> drawn to same scale. The horizontal dotted lines indicate the boundaries of 

 similar Life Zones. 



