66 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



The earliest Wasatch sediments are those in the 

 Big Horn and Clark Fork Basins of northern Wyoming, 

 from which we obtain the whole range of lower Eocene 

 fossil mammals, beginning with the end of basal 

 Eocene time. 



fossils. Douglass found a considerable faima in the 

 Wasatch of the Uinta Basin. Systemodon occurs 

 there. Wortman has reported (letters) a Coryphodon 

 from the Wasatch of the Washakie Basin. To the 

 south, in the San Juan Basin, there were laid 

 down, over the Torre j on, thick beds of sand 

 and fluviatile sediments, which form the New 

 Mexico Wasatch. These beds, which are 

 divided by Granger (1914.1) into an upper 

 ("Largo') and a lower ("Almagre") divi- 

 sion, have a combined thickness of 1,500 feet, 

 throughout the greater part of which mam- 

 malian fossils are found. These Wasatch beds 

 in New Mexico have much the same general 

 appearance as the Wasatch in other localities, 

 consisting of red, gray, and ocherous bands 

 of shale and sandstone, without evidence of 

 unconformity throughout the series. The most 

 recently identified Wasatch sediments are 

 those of Pumpkin Buttes, in the Powder 

 River Basin, Wyo. 



The correlation of the faunal horizons in 

 these sedimentary areas by the species of 

 mammals which they contain was determined 

 with remarkable precision by the American 

 Museum expedition under Granger, as shown 

 in the accompanying table (p. 67). 



Wasatch pJiysiograpliic and climatic condi- 

 tions favorable to modernized fauna. — All the 

 Wasatch sediments indicate a profound and 

 somewhat abrupt change in the physiographic 

 and climatic conditions of the mountain-basin 

 region from those that prevailed during Fort 

 Union, Puerco, and Torrejon time. In general, 

 still-water sedimentation in level forests and 

 lagoons ceased. Fluviatile, flood-plain, fluvial- 

 fan, and channel deposits containing a larger 

 percentage of coarser materials were wide- 

 spread. There is evidence of open stretches 

 of country exposing sand, gravel, and clay, 

 subject to occasional desiccation and aridity. 



The Wasatch of the Big Horn Basin repre- 

 sents the filling of an intermontane trough of 

 downwarp. (Sinclair and Granger, 1912.1, 

 p. 66.) Materials were transported by streams 

 Figure 44.— Columnar section of Cretaceous and Eocene sediments ex- f ^.^^ ^^le surrounding mountains, as shown by 

 posed -along Bear River near Evanston, in extreme southwestern ^^e lithology of the gravel, sand, and clay. The 



Wyoming (No. 3, fig. 35) , sliowing tlie typical Wasatcli group of Hayden 

 (1869). Chiefly after A. C. Veatch (1907.1) 



Mammals similar to those in zone 8 (Eohippus, Phe-nncodus, lieplodon, and Coryphodon) occur 

 in a narrow fossiliferous stratum which may be referred to the Heptodon- Coryphodon- Eohippus 

 zone. Above are Oreen River and Bridget beds; below are 4,600 feet of beds (without mammals) 

 belonging to the Wasatch group (Fowkes and Almy formations), which are imderlain by the 

 Evanston formation, containing Fort Union plants, and the AdaviUe formation, containing 

 Montana plants and invertebrates. The author of this monograph regards the Evanston 

 formation as uppermost Cretaceous. 



Similar heavy and continuous sedimentation also 

 occurred during Wasatch time, in both the northern 

 and the southern Uinta region, in the Bridger and 

 Washakie Basins on the north, and in the great Uinta 

 Basin south of the mountains. Few of these vast 

 masses of sediment have thus far yielded mammalian 



underlying Fort Union was uplifted before 

 sedimentation began, and the synclinal basin 

 was inclosed more or less completely to the east, 

 south, and west by anticlinal mountains. 

 Erosion from the mountain rocks represents 

 all the members of the typical section from 

 the Archean to the Fort Union, usually 

 by stream transportation and deposition in river 

 channels and over broad flood plains. No beds of 

 volcanic ash have been found, nor is there evidence 

 of transportation by wind. The deposits of clay show 

 a more or less regular alternation of red and bluish- 

 gray layers, which may be due to climatic changes. 



