FORMATIONS AND PHYSICAL HISTORY 



589 



in the south. As in most other post-Paleozoic systems, non-marine 

 formations have much representation in this. The marine beds are 



Fig. 495. Petrified tree-trunks, Yellowstone National Park. (Iddings. U. S. 

 Geol. Surv.) 



chiefly along the Atlantic and Mediterranean. In the north, much 

 of the system is buried beneath glacial drift. Thick conglomerates 

 (3,900-5,900 feet) of early and middle Miocene age are found 



