ENVIEONMENT OF THE TITANOTHEHES 



73 



annual rainfall exceeding 200 centimeters. This flora 

 is not very difl'erent from that found in the upper 

 Ypresian of France. 



These forests are so interesting in respect to the 

 environment of the first titanotheres which appeared 

 in North America that the principal genera cited by 

 Berry may be quoted in full. The figures 

 appended to the names of the genera 

 show the number of species in each genus. 



(Sinclair and Granger, op. cit., p. 105.) There is 

 evidence also of an uplift of the Big Horn Range 

 subsequent to the deposition of the Wasatch. In 

 the Wind River Basin material washed down from 

 the mountains continued to be spread over the basin 

 floor by streams until the end of upper Eocene time. 



Acrostichum, 1. 

 Alnus, 1. 

 Ampelopsis, 1. 

 Aralia, 1. 

 Arundo, 2. 

 Brasenia?, 1. 

 Cheilanthes, 1. 



Eucalyptus?, 1. Myrica, 1. 



Ficus, 4. Phragmites, 1. 



Ilex, 2. Planera, 2. 



Juglans, 3. Quercus, 2. 



Leguminosites, Rhus, 1. 



1. Sabal, 1. 



Lygodium, 1. Salix, 2. 



Cissus, 1. Manicaria, 1. Sapindus, 1. 



Cyperus, 1. Musophyllum, Sphaeria, 1. 



Equisetum, 1. 1. Zizyphus, 2. 



The Green River flora is the only de- 

 scribed middle Eocene flora known from 

 latitude 40°. The nearly contempora- 

 neous Claiborne flora of Georgia shows 

 (Berry, op. cit., p. 161) that the main 

 elements of the modern flora of tropical 

 America reached at least as far north as 

 latitude 33° and, in the middle Eocene, 

 probably several degrees farther north. 



Wasatch and later events. — In areas that 

 lay north of the great lake in this region 

 in Wasatch time were laid down the sedi- 

 ments of the Wind River and Big Horn 

 Basins, the deposition of which began in 

 the first phase of Wasatch time and prob- 

 ably continued into middle Oligocene 

 time. (Sinclair and Granger, 1911.1, p. 

 85.) The Wind River sandstones in the 

 vicinity of the Beaver Divide are stream- 

 channel deposits, probably laid down in 

 broad, shifting streams of low gradient 

 which flowed across clay-covered flats, 

 into which they sunli their channels or 

 over which in seasons of flooding they 

 spread coarse detritus. The materials 

 composing these sandstones were derived 

 from the granites and other pre-Ter- 

 tiary rocks of the surrounding moun- 

 tains. Below the Lambdoiherium zone 



Figure 49. — Map showing cluster of lower, middle, and upper Eocene sedi- 

 mentary basins in southwestern Wyoming and northern Utah, exhibiting 

 parts of areas of the Wasatch, Wind River, Bridger, and Uinta formations 

 at other localities, interstratified with Extensive areas of the Wasatch are purposely omitted. After Osborn and Matthew (1909.321), U. S. 



Wi T~» • 1 1 ^ A ,1 Geol. Survey Bull. 361. Arrows show lines along which sections were taken 



md River clays and sandstones, there 



are layers of white volcanic tuff, 13 feet thick, in- 

 dicating the presence of active volcanoes. The floor 

 of the Big Horn Basin, to the north, was modified 

 by erosion that took place subsequent to the main 

 uplift of the Big Horn Mountains, which occurred 

 after the deposition of the Fort Union formation. 

 101959— 29— VOL 1 7 



Fluviatile and flood-plain deposition is indicated 

 throughout Eocene time. The lignitic shales that 

 cap the Lamhdof-herium zone of the Big Horn Basin, 

 containing fresh-water mollusks (Planorhis) and crus- 

 taceans (Entomostraca), are certainly both fluviatile 

 and palustrine. 



