THE EOCENE OF NORTH AMERICA 445 



The Eocene deposits of western North America may be 

 divided into three groups, namely, those laid down in fresh water, 

 those laid down in brackish water, and those laid down in sea 

 water. * To these should probably be added those_deposited by 

 streams, though this class of formation has not been generally 

 differentiated from the first. 



1. The fresh-water deposits stretch with many interruptions from 

 New Mexico and Colorado northward and nothwestward through 

 Utah, Wyoming, Montana, North Dakota, the Dominion of 

 Canada, to the Arctic Circle and probably the Arctic Ocean. 

 The formations belonging to this area are the Fort Union, which 

 is the Upper Laramie of the Canadian Geological Survey, the 

 Kenai, Puerco,Torrejon, Wasatch, Bridger, including Green River, 

 Uinta, Huerfano, Mojave, Amyzon, and Manti. In addition 

 there are non-fossiliferous conglomerates which are supposed to 

 be of Eocene age, as follows : Sphinx conglomerate, Pinyon 

 conglomerate, and San Miguel conglomerate. 



2. The brackish-water deposits extend with interruptions from 

 Oregon through Washington into British Columbia. The forma- 

 tions belonging to this group are Arago and Puget. 



3. The marine deposits in Oregon and California. The forma- 

 tions belonging to this group are Tyee, Umpqua, Martinez, and 

 Tejon. 



In the following pages the known data concerning the dis- 

 tribution and nature of these several formations is summarized, 

 and their correlation as determined by various investigators 

 indicated. 



THE FRESH-WATER BEDS. 



THE FORT UNION FORMATION. 



The Fort Union beds are named from a former military fort 

 on the Missouri River in North Dakota where they are typically 

 exposed. They occur in North Dakota, Montana, extending 

 thence north and northwest into Canada and with interruptions 

 to the Arctic Circle and probably to the Arctic Sea. These 

 beds are thus described by Meek and Hayden 1 : "Beds of clay 



'Quoted by Clark, U. S. Geol. Surv., Bull. 83, p. 113, 1891. 



