136 



GEOLOGICAL HISTORY OF THE YELLOWSTONE PARK. 



close of the Cretaceous, altliougli there is good reason to believe that 

 in this region profound fanlting and displacement continued the work 

 of mountain building well into the Middle Tertiary period. 

 Throughout Tertiary time in the Park area, geological history was char- 



sc.iic:iiueh=vju,ncs. YELLOWSTO>'E JiATIONAL PARK 



acterized by great volcanic activity, enormons volumes of erupted mate- 

 rial being jwured out in theEocene and Middle Tertiary, continuing with 

 less force through the Pliocene, and extending into Quaternary time. 

 Within very recent times there is no evidence of any considerable out- 



