FORT UNION OF CRAZY MOUNTAIN FIELD, MONT. 7 



to which it was due have made the subject of Paleocene mammals an 

 obscure one, generally avoided, but they have also made it a particu- 

 larly fruitful field for research in recent years. 



The first Paleocene mammalian fauna to be discovered was that of 

 the Thanetian, or particularly of its subdivision the Cernaysian, in 

 France. Arctocyon primaevus was described by Blainville in 1841, but 

 knowledge of the fauna really dates from Lemoine's pubhcations 

 beginning in 1878. It has only recently been revised and placed on a 

 satisfactory basis by Teilhard (1916, 1921). 



The American Puerco formation of New Mexico was named in 

 1875 but yielded no mammals until 1881, when the famous collector 

 David Baldwin began a long collecting campaign there for Cope. This 

 work has been followed, since 1892, by a series of expeditions to this 

 field under Wortman, Granger, Sinclair, Simpson, and others for the 

 American Museum of Natural History, which also acquired the Cope- 

 Baldwin collection. This stratigraphic sequence in the San Juan 

 Basin of New Mexico has become the standard of comparison for the 

 Paleocene of the world, and its faunas are far the best known and 

 represented by the most nearly perfect specimens (although in variety 

 they do not exceed those to be described in tliis memoir). They have 

 been described by Cope, Osbom, Earle, Wortman, Matthew, Granger, 

 Simpson, and others and are thoroughly revised in a memoir by 

 Matthew (Pale. Mem.), published while this bulletin was in press. 

 Three quite distinct formations and faunas have been recognized, 

 Puerco, Torrejon, and Tiffany, the first two each with two well-marked 

 separate faunal zones of different facies but nearly the same age. 



The Fort Union group was originally defined by Meek and Hayden 

 (1861) as occupying ''the country around Fort Union,^ extending north 

 into the British possessions to unknown distances; also southward to 

 Fort Clark. . . , Seen under the White River group on North Platte 

 River above Fort Laramie. Also on west side of the Wind River 

 Mountains. . . . and also occupying extensive areas of country in 

 Nebraska . . . and beneath the White River group at several distant 

 locahties." Although the designation of the type locality leaves no 

 doubt as to the inclusion of certain strata in the group or as to its 

 general position in the scale, the name has been used in man}^ different 

 ways, and in keeping with the spirit of the original description it has 

 been applied to any or all strata at about tliis part of the geologic 

 section, that is, in what we now call Paleocene, over a very large area 

 in the Northwest. Thanks to this widespread occurrence or use of the 

 name, and to the economic value of these rocks, especially as a coal- 

 bearing series, few geologic formations have been more intensively and 

 extensively studied. No general review of this work is here attempted _ 



* Near the present site of Buford, N. Dak. 

 119212—37 -2 



