102 
ORIGIN OF LIFE IN AMERICA 
the most valuable and extensive 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. 122—136. 
t Whitney, J. D., “ Climatic Changes,” pp. 64 — 72. 
