ENVIRONMENT OF THE TITANOTHERES 



91 



AMVNODON SANDSrONE 



large number of identical species, and therefore con- 

 stitute an extension of the Eobasileus-DolichorMnus 

 and Metarhinus life zones to the south. The fauna 

 and deposits of Uinta B are more fully described on 

 pages 91-99, in the description of the Uinta Basin. 



UINTA BASIN, UTAH 



PHYSIOGRAPHIC, CUMATIC, AND VOLCANIC CONDITIONS IN THE UINTA 

 BASIN DURING MIDDLE (?) AND LATER EOCENE TIME 



It is a striking fact that the later Eocene sediments 

 in the Uinta Basin are composed mainly of altered 

 eruptives, probably dacite 

 tuffs, as indicated by analyses 

 of nine samples by Johannsen 

 (1914.1, pp. 212-214). The 

 rocks of the lower levels ^ 

 described as "brown sand- 

 stones" comparable in litho- 

 logic appearance to Washakie 

 A, contain a large element of 

 tuff and consist microscop- 

 ically of irregularly broken 

 and rounded fragments of 

 quartz, lime-soda feldspar, 

 hornblende, biotite, and frag- 

 ments of andesite or basalt in 

 a brown groundmass, which 

 is chiefly chlorite but contains 

 some calcite. On the lower 

 levels (in Uinta A) brown is 

 the prevailing color, as in 

 Washakie A. In Uinta B 

 sediments of this color pass 

 into pinkish-brown and red- 

 dish-brown sediments, and in 

 Uinta C into pale-green and 

 gray fine-grained rocks con- 

 taining considerable glass. 

 Many rocks that look like 

 sandstones prove under the 

 microscope to resemble flow 

 breccias. 



Uinta A as now defined is entirely unfossiliferous 

 but is here correlated with the middle Eocene fossil- 

 iferous horizon A of the Washakie Basin {Uintathe- 

 rium zone). 



Uinta B 1 (in some previous reports included in 

 Uinta A) contains a rich river-border fauna, like that 

 of Washakie B 1. 



Uinta B 2 (formerly constituting all of Uinta B) 

 contains a larger land and river-border fauna, like 

 that of Washakie B 2. 



BARREN 



{DiplacodoTV- 

 EpUtippus 

 zone 



EobcLsiZeus - 



DolichorTuruLS 



zoTte 



TYPICAL U/NTA MEADOW FAUNA 



TRANSITION FAUNA 



^:metarhinus sandstone" 



'XfluviatiTe' ^=r 



£^?^ ^_^1 MetarhiniMS 



FLU VI ATI LE FAUNA 



Figure 63. — Diagrammatic section of the Uinta formation exposed in tiie nortii wall of 

 White River Canyon 3 miles below mouth of Evacuation Creek, Utah 



GEOLOGIC HORIZONS IN THE UINTA 

 BASIN 



Uinta fauna of Marsh 100 feet above "Amynodon sandstone." 



The deposits of horizons 

 A and B of the Uinta Basin 

 are not those of the typical Uinta formation of Marsh 

 (1871.3), of King (1878), or of Scott and Osborn 

 (1891.1), all of which belong to Uinta C, the Diplaco- 

 don zone; they form the lower part of the section 

 (Uinta A and Uinta B), determined by the American 

 Museum expedition of 1894 under Peterson (Osborn, 

 1895.98) and successively explored with remarkable 

 results by Peterson, Douglass, and Riggs, whose obser- 

 vations and exact records of the vertical distribution 

 of genera and species have firmly established the 

 stratigraphy of the Uinta Basin section as presented 

 in Figure 65. (See PL IX.) 



After observations of Peterson, Douglass, and Riggs. Uinta A, columnar sandstones, unfossiliferous; Uinta B 1, MetarUnus 

 zone capped by ** Metarhinus sandstone," containing a fiuviatile fauna; Uinta B 2, Eobasileus-DaUchorhinus zone, capped 

 by "Amynodon sandstone," containing a transition fauna; Uinta C, Diplacodon-EpiMppus zone, containing the typical 



Uinta C contains the typical Uinta (Diplacodon) 

 fauna. 



The sediments in the Uinta Basin between the 

 Diplacodon zone and the Green River formation were 

 classified by White (1878.1, p. 37) as Bridger, although 

 no fossils were found in it, and wore treated as con- 

 temporaneous with the Bridger deposits. We now 

 know that the sediments that form Uinta B were cer- 

 tainly laid down after Bridger C and D had been 

 deposited, but they may have been contemporaneous 

 with the unfossiliferous Bridger E. During the 

 American Museum explorations of 1893-94 Peterson 



