22 



CENOZOIC MAMMAL HORIZONS 



(fig. 15, p. 82). This succession of depositions and erosions has ren- 

 dered the Tertiary geologic history of the Great Plains very compli- 

 cated, and has retarded our geologic and paleontologic solutions. 



Fourth, owing to the proximity of the volcanic zones, volcanic ash 

 and other fine eruptive materials contributed very largely and in 

 some basins almost exclusively to the Eocene and Oligoeene deposits 

 in the Mountain Kegion, while in the Plains Region, which was 

 more distant from the active craters, volcanic-ash deposits were 

 occasional, and conglomerates, sandstones, and clays make up the 

 main mass of the deposits. In some Plains deposits, however, vol- 

 canic ash is a large component. 



Fifth, the mammalian life of the Mountain Region was largely 

 that of plateaus, uplands, and elevated basins, of streams and lake 

 borders, of hillsides, and more or less of the forests. The mammalian 

 life of the Plains Region was that of savannas and pampas, of broader 

 plains and rivers, with more restricted forests. There was, however, 

 no sharp life demarcation, because then, as now, some of the Plains 

 types penetrated the Mountains and some of the Mountain types 

 penetrated the Plains. 



General homotaxis of some of the Mountain and Plains formations. 



MOUNTAIN BASIN DEPOSITS. 



GeoZofif^c— Partly of erosion 

 materials; largely of vol- 

 canic materials, partly 

 eolian, partly deposited 

 in water. 



Faunistic .—'E-Ktinct mam- 

 mals, chiefly inhabiting a 

 mountainous, hilly, for- 

 ested, lake- and river- 

 border, wel l-watered 

 country. 



GREAT PLAINS DEPOSITS. 



Geologic— 'L&Tg&lj of wa- 

 ter-erosion and wind-ero- 

 sion materials; partly of 

 volcanic materials. 



Faunistic— Extinct mam- 

 mals, chiefly of an open- 

 plains country, traversed 

 by broad, slow-moving 

 rivers, savanna, partly 

 forested, with shallow 

 lakes and decreasing rain 

 supply. 



Middle Pliocene. 



Lower Pliocene or j 



upper Miocene. 

 Upper Miocene j Rattlesnake, Oreg. 



I 



Middle Miocene 



Lower Miocene and 



Deep River,Mont.;Mascall, 

 i Oreg. 



1 1" Fort Logan," Mont 



xJohn Day (upper part), 



upper Oligoeene. jj^ ^^^^ 



Upper Oligoeene .. . John Day (middle and 



lower part,s), Oreg. 

 Lower Oligoeene. . . Deposits on Pipestone 

 Creek, Mont. 



Upper Eocene. 

 Middle Eocene 

 Lower Eocene 

 Basal Eocene. 



Blanco, Tex 



Ogalalla, in part ("Repub- 

 lican River"), Nebr. 



Ogalalla ( ' ' Nebraska ") 

 Nebr. 



" Pawnee Creek," Colo 



Arikaree (Gering Rose- 

 bud), Nebr. 



White River, S. Dak. (upper 

 part). 



White River (lower part), 

 of the western plains, of 

 South Dakota, Nebraska, 

 etc. 



Uinta, northern Utah 



"Washakie," Wyo 



Bridger, Wyo 



Wind River, Wyo j 



Wasatch, N.Mex. and Wyo 



iTorrejon, N. Mex 



<Puerco, N. Mex 



I Fort Union, Mont 



Second deposition pe- 

 riod of very wide- 

 s pre ad fluviatile, 

 flood-plain, and eoli- 

 an deposits, chiefly 

 erosion and volcanic 

 materials, on the 

 Great Plains of Da- 

 kota, Nebraska 

 Colorado, and west- 

 ern Kansas. Limit- 

 ed and scattered 

 deposits in the 

 Rocky Mountain 

 region. 



First deposition (or 

 Eocene) period of 

 lacustrine, river, and 

 flood-plain deposits, 

 largely of volcanic 

 materials in the 

 Rocky Mountain ba- 

 sin, chiefly in the 

 ancient drainage ba- 

 sin of Colorado Riv- 

 er. Plains deposits 

 of this period eroded 

 away, buried, or un- 

 known. 



