DEVELOPMENT OF UINTA SANDSTONE. 141 



UINTA GROUP. 



As shown by the map, the great mass of the Uinta Range is composed 

 of sandstones of this group. Intercalated with the sandstones some shales 

 are found, the latter being arenaceous, with a small portion of argillaceous 

 material. In a few places the sandstones have assumed a crystalline struc- 

 ture, forming a quasi quartzite. The whole group is exceedingly ferruginous. 

 Thin seams of clay ironstone are often seen to separate the strata of sand- 

 stone, and many of the shales contain large quantities of iron. Many of the 

 sandstones are seen to be ferruginous on the interior when broken, but some 

 of the beds are buff and light gray on fresh surfaces. The general color 

 of the walls of the canons and mountain escarpments is red and brown, due 

 to the more complete oxidation of the iron. In the canons and gulches, 

 where bays of quiet water are formed, considerable accumulations of steel- 

 gray iron sands may often be seen. These sometime form a pigment which 

 the Indians of the region were accustomed to use as paint in former days. 



The great mass of the sandstones are fine grained, but occasionally 

 throughout the series .strata of pebbles are found; near its junction with 

 the Red Creek Quartzite these are conglomerates. Those peculiarities or 

 markings of strata, known as ripple marks, are very abundant at many hori- 

 zons from the top to the lowest known strata and mud rills, and rain drop 

 impressions are sometimes found. A very few concretions have been found 

 in the group. Weeks and months have been spent in the search yet no fos- 

 sils have been found. Within the territory embraced in the description the 

 base of the group is never seen. The Green River runs along the axis of 

 the Uinta flexure for many miles but its bed is yet in the Uinta Sandstone 

 so that it is impossible to determine the entire thickness of the group, but 

 that which is exposed has a wonderful developement, no less than 12,500 

 feet of these sandstones and shales being 1 seen. 



I have already stated my reasons for considering this formation to be 

 older than Carboniferous, and I have given it provisionally a Devonian color 

 on the map. Professor Marsh in his article in the American Journal of 

 Science and Arts, in the March number of 1871, "On the geology of the 

 eastern Uinta Mountains," in speaking of these formations says, " * * * * 

 and a subsequent examination of apparently a portion of the same series, 



