64 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



Figure 3. Sketch map of region embracing the Yellowstone Park (sho^sTi by- 

 rectangle on the 110th meridian); after Iddings. Small circles represent an- 

 desitic pyroclastics and flows of Eocene and Miocene age (central eruptions). 

 Horizontal lines (map in usual orientation) represent Pliocene rhj'olite of the 

 Park (eruption chiefly by foundering). Vertical lines represent the Pliocene 

 Snake River basalt (fissure eruption). 



