THE EOCENE PERIOD. 209 



or subaerial, or both. In the several areas, the sedimentation was 

 partly contemporaneous and partly successive. One area of depo- 

 sition was in the Wind River basin, north of the mountains of that 

 name. Later, deposition was in progress in the basin of the Green 

 River in Wyoming, and also in the basin of the same river south of 

 the Uintas. In these areas, beds of sediment, said to be locally as 

 much as 2500 feet thick, were deposited. 1 The materials are chiefly 

 clastic, though there is not a little calcareous matter in some places. 2 

 It may have been during this stage that the formation of volcanic 

 tuff (San Juan, 2000 feet and less in thickness) of the Telluride region 

 was made. 3 This formation is of interest as an index to the vigor of 

 volcanic action in this region. At about the same time, the Huerfano 

 formation, of Colorado, estimated to have a thickness of 3300 feet, 

 was laid down. At the close of this stage there was some defor- 

 mation in southern Colorado, where the beds already deposited were 

 tilted. In some places (Sangre de Cristo range) mountain -making 

 was in progress. 4 



4. The Uinta (perhaps Jacksonian) stage 5 followed the Bridger. 

 Crustal movements, or the progress of gradation, or the effects of 

 vulcanism, or all together, seem to have shifted the sites of sedimenta- 

 tion from the areas where the Bridger beds were deposited, to an area 

 lying mostly south of the Uinta mountains, in southeastern Utah 

 and southwestern Colorado. The area of the Uinta deposits occupied 

 a part of the area covered by the Wasatch and Bridger formations, 

 and where this was the case, the Wasatch, Bridger, and Uinta beds 

 are found in superposition. The Uinta beds now have an altitude 

 of 10,000 feet, though they may have been deposited at a much lower 

 level. 6 At the close of this stage, the new-made deposits were tilted 

 and somewhat deformed. 7 



Eocene deposits of lacustrine or subaerial origin are known at numer- 



1 King, op. cit. 



2 King, op. cit,, p. 381. 



3 Purington, Telluride, Colo., folio, U. S. Geol. Surv. 



4 Hills, Walsenburg folio, U. S. Geol. Surv. 



5 Here belong the Diplacodon beds of Marsh and the Browns Park group of Powell; 

 Geol. of the Uinta Mountains, pp. 63, 168, 208. 



6 It is possible that some of these beds should be referred to the Oligocene stage 

 of the period. 



7 King, op. cit., p. 448. 



