102 OKIGIN OF LIFE IN AMEEICA 



the most valuable and extemdve deposits of fossils in 

 existence.* 



As we enter the United States, proceeding along the Rocky 

 Mountains, we soon find ourselves in the midst of the Miocene 

 and the lower Oligocene beds (White River) of Montana. 

 Further south, in Wyoming, we come to the Wind River beds, 

 while on our left to the east lie the Wasatch deposits, both 

 of which belong to the lower Eocene. Westward we cross 

 into the middle Eocene Bridger and Washakie beds of 

 Wyoming, and also the upper Eocene Uinta of Utah. Much 

 further south we finally meet with the famous Puerco, Tor- 

 rejon and Wasatch formations of the San Juan basin in New 

 Mexico, which are held to be of basal and lower Eocene age. 

 Owing to the labours chiefly of Leidy, Marsh, Cope, Scott, 

 Osborn, Wortman, Matthew, Hatcher, and others, a most re- 

 markable assemblage of fossils has been obtained among these 

 immensely rich deposits. Our knowledge of the former 

 inhabitants of North America has thus greatly increased 

 within recent years, and has aided us in tracing the gradual 

 changes of land and water that the continent has undergone 

 in past times. Great efforts are now being made to work out 

 the correlation of the North American mammal -bearing 

 horizons. I propose to return to this subject later on, and 

 need not dwell on it any longer at present. 



Although glaciers have now almost entirely disappeared 

 from the Rocky Mountains, abundant proofs have been left 

 of their past presence in the shape of moraines, and polished 

 as well as striated surfaces. These signs of former glaciation 

 are very different from the thick mantle of drift that we 

 noticed in Canada, and which is likewise attributed to the 

 action of glaciers. Only the highest summits and the most 

 elevated valleys of the Rocky Mountains were ever occupied 

 by ice, and there does not appear to be any sign of a 'deposit 

 in the whole range resembling the northern drift.f 



These glaciers, no doubt, owed their existence to a greatly 

 increased precipitation of moisture in the Rocky Mountains 

 during the Ice Age, for we possess quite an unmistakable 



* Russell, I. C., " North America," pp. 122136. 

 t Whitney, J. D., " Climatic Changes," pp. 6472. 



