TITANOTHEEES OP ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



tensive geologic researcli than tlie interpretation of 

 the Oligocene sediments. The program for this 

 exploration was proposed by the author to the Director 

 of the United States Geological Survey in 1900. 



Each of the typical lower, middle, and upper Eocene 

 basins shown in the accompanying map has had its 



Wind River Valley. Also west of Wind River Moun- 

 tains." It is possible that Hayden here refers to the 

 Wasatch or the Bridger formation, which lie southwest 

 of the Wind River Range. 



Subsequent exploration by Hayden revealed the 

 typical Bridger, Wasatch, and "Washakie"^ forma- 

 tions, each affording portions of separate 

 chapters in the history of the ancient 

 mammalian life of the mountain-basin 

 region, which has proved to be no less 

 remarkable than that of the Great Plains. 

 Hayden was aided by the early paleon- 

 tologic observations of Leidy on the 

 Bridger fauna. 



The survey along the fortieth parallel 

 by Clarence King was supplemented by 

 the paleontologic observations of Marsh, 

 who described the life areas south of 

 the Uinta Mountains and defined the 

 Diplacodon zone of the Uinta. Cope 

 hastened to describe the life of the Wind 

 River, of the Wasatch, and of the 

 "Washakie" formations and made known 

 a very rich fauna contemporaneous with 

 the Wasatch of the Big Horn Basin, to 

 the north, and of the San Juan Basin of 

 northern New Mexico, to the south, where 

 he also discovered the basal Eocene fauna 

 (Puerco). Five of these six geologic for- 

 mations were long regarded also as fau- 

 nistic units and were described as single 

 life zones, namely, the "Diplacodon beds" 

 (Uinta formation), the "Dinoceras beds" 

 (Bridger and "Washakie" formations), 

 the " LambdotJierium beds" (Wind River 

 formation), the " Coryphodon beds" 

 (Wasatch formation), and the Puerco 

 formation. 



The intensive observation of these 

 six formations and the analysis of their 

 fauna has enabled us to divide them 

 into sLxteen known life zones, which in 

 turn afford the key to the time of origin 

 and of cessation of sedimentation in each 

 basin. 



Figure 9. — Map showing cluster of typical lower, middle, and upper Eocene 

 sedimentary basins in the heart of the Rocky Mountain region 



DISCOVERY AND DELIMITATION OF PERIODS 

 OF SEDIMENTATION AND OF LIFE ZONES 



Mapped chiefly aftst the explorations of Hayden, King, and Powell of successive Government 

 surveys. The arrows indicate the lines along which were taken the chief geologic sections de- 

 scribed and illtistrated in Chapter II. Modified from Osbom and Matthew, 1909.321. 



antecedent historic and its recent analytic treatment, 

 beginning with the Wind River deposits of Hayden 

 (Meek and Hayden, 1862.1, p. 433), who described 

 these deposits as "light-gray and ash-colored sand- 

 stones, with more or less argillaceous layers. Fossils — 

 fragments of Trionyx, Testudo, with large Helix, 

 Vivipara, petrified wood, etc. No marine or braclcish- 

 water types * * * 1,500 to 2,000 feet * * * 



The fact that these sediments ac- 

 cumulated very slowly, during long 

 periods of geologic time and in the course of profound 

 changes in climatic and physiographic environment, 

 with consequent variations in the fauna and flora, 

 has gradually become recognized, and the explorations 

 and researches that have led to this recognition have 



s The Washakie was contemporaneous with the upper two-thirds of the Bridger 

 formation, and the name Washakie is now abandoned by the United States Geolog- 

 ical Survey for the name Bridger. 



