Emery — Green River Desert Section, Utah. 573 



stone, or Mancos shale where the Dakota is absent. The 

 formation embraces a series of coarse sandstones, con- 

 glomerates and variegated marl-like shale, and may be 

 divided into, three parts on the basis of lithology. Of 

 these the lowest consists of coarse sandstone and con- 

 glomerate with minor amounts of light shale and has been 

 called the Salt Wash member, by Lupton. 24 The middle 

 portion embraces a series of variegated shales with local 

 thin sandstones, and the upper portion consists of hard 

 sandstone which weathers dark and has associated with it 

 small amounts of variegated shale. 



At the base of the Salt Wash member of the McElmo 

 formation is 15 to 20 feet of light variegated shale which 

 contrasts strongly in lithology and color with the under- 

 lying Navajo sandstone. The Salt Wash member is 200 

 feet thick, and with the exception of the basal shale, con- 

 sists of coarse sandstone composed of loosely cemented, 

 rather well rounded quartz grains mostly translucent 

 with a small per cent of weathered feldspar. It also 

 includes considerable poorly cemented conglomerate. 

 These rocks are light-colored on fresh fracture and in 

 many places weather nearly white, though elsewhere they 

 weather a light brownish color. Fragments of light-col- 

 ored petrified wood are present in this series and with 

 them are associated in a number of places yellow streaks 

 in irregular blotches of carnotite, and other uranium and 

 vanadium ores. Many uranium claims have been located 

 on the outcrop of this part of the formation in the vicinity 

 of San Rafael River and numerous prospect holes have 

 been opened. The Salt Wash member also includes 

 numerous fragments of dinosaur bones which differ from 

 the dinosaur bones in the overlying beds in that they 

 are smaller. 



The presence of shale very different in character from 

 the underlying Navajo beds, and the further presence of 

 a considerable thickness of conglomerate and coarse sand- 

 stone indicates that deposition in Salt Wash time took 

 place under conditions entirely different than those pre- 

 vailing before that time. The evidence indicates that 

 Salt Wash deposition was separated from the Navajo by 

 a time break, and that the contact of the Navajo and 

 McElmo is unconformable. 



24 Lupton, C. T., Oil and gas near Green Eiver, Grand Comity, Utah, TJ. S. 

 Geol. Survey, Bull. 541-D, p. 15, 1914. 



