272 



GEOLOGY. 



Park, 1 where evidences of Miocene volcanic activity are to be seen 

 on all hands. Locally, 2 forests were buried by the volcanic ejecta, 



Fig. 450. — Petrified tree-trunks, Yellowstone National Park. 

 (Iddings, U. S. Geol. Surv.) 



and in favorable situations their trunks were petrified (Fig. 450). 

 Great areas of the sedimentary beds of the period are concealed by 



1 See western folios, U. S. Geol. Surv., notably the Yellowstone National Park 

 folio. Most of the folios showing Neocene formations show Volcanic rocks of Neocene 

 age. 



2 Yellowstone National Park folio. 



