Mesozoic and Ccenozoic Geology and Palceontology. 179 



Parks. In the area of the San Juan they arc the only rocks exposed 

 l^etween Macomb's trail and the New Mexico line, excepting the snaall 

 patch of Triassic, on the Rio Florida, and Rio de las Animas. The 

 Tocks differ in detail, but as a whole, the series is made up of three 

 •divisions. The lower is a mass of sandstone 200 to 500 feet thick; 

 the middle is composed of shales and limestones, with, in the eastern 

 localities, marls and sandstones 1,000 to 1,500 feet; and the upper, 

 ■chiefly sandstones, with intercalated shales and lignites 500 to 700 

 feet. 



He referred the whole lignite bearing series exposed at Canon 

 dity, and at other localities along the eastern base of the Rocky moun- 

 tains, to the upper Cretaceous. 



In 1876, Prof. J. W. Powell* separated the Cretaceous rocks of th€ 

 Plateau Province of the west, in ascending order, as follows: 



1. Henry's Fork Group, 500 feet. 



% Sulphur Creek Group, 2,050 feet. 



3. Salt Wells Group, 2,000 feet. 



4. Point of Rocks Group, 2,000 feet. 



The Henr^^'s Fork Group consists of sandstones, bad land rocks, con~ 

 ;glomerates and shales, with carbonaceous shales and lignitic coal. 

 It has an out-crop parallel and approximately co-extensive with the 

 Triassic and Jurassic; that is, like those groups, it was brought up 

 by the great Uinta upheaval, and the elevation of the Yampa Plateau. 

 The conglomerates have a much more extensive development on the 

 south than on the north side of the Uinta mountains. On the south 

 side of the Yampa plateau, where the Fox creek and Cliff creek flex- 

 ures unite, the}' stand on edge, with a dip of about 85° to the south- 

 east, and are firmly cemented^ and stand as high walls, separated by a 

 long, narrow vallej^, strewn with fragments of the conglomerate which 

 have tumbled down from either side. 



The Sulphur Creek Group consists of black shales, occasionally 

 friable sandstones with carbonaceous shales and lignitic coal. It is 

 well exposed near Hitliard station, on the Union Pacific railroad, in 

 the hills cut by Sulphur creek; there are many fine exposures on the 

 north and south sides of the Uinta mountains ; on Henry's Fork ; between 

 the head of Dry Lake valley and Vermilion creek; in the Escalante 

 valley, Paria valley, Kanab valley, and many other localities. 



The Salt Wells Group consists of sandstones or arenaceous shales; 

 often ver}' friable, producing bad lands, with carbonaceous shales and 



''•• Geo. of Uinta Mountains. 



