THE SEDIMENTARY KECORD 441 



have never been studied in detail, and but little definite data regarding 

 their lithologic or stratigraphic divisions are available. Blufiis and ridges 

 of these strata from the sides of the alluvial valleys and small remnants 

 occur along the mountain slopes, reaching elevations of over 10,000 feet. 

 Along the south side of the range the lower members are grits and con- 

 glomerate passing into finer grained sandy and calcareous beds. 



Interpretation op the sedimentary Eecord 



No representative of the basement complex is known in the Uinta 

 region. The 12,000+ feet of the "Uinta" formation, 1,200 feet of 

 Lodore shales, and 1,100 feet of the Ogden quartzite have not yielded 

 fossils. On lithologic and stratigraphic grounds the "Uinta" formation 

 is considered to represent the sediments of pre-Cambrian time. The Lo- 

 dore shales represent a period of sedimentation in which from 2,000 to 

 4,000 feet of Lower, Middle, and Upper Cambrian shales and limestones 

 were deposited in the Central and Northern Wasatch and Grand Canyon 

 sections. In the Wasatch region approximately 3,000 feet of limestone 

 and quartzite were deposited in Ordovician time, while in the Uinta 

 region a maximum of 1,100 feet of sandy beds were laid down during the 

 same period. On the northern flanks of the Uinta range, in the Green 

 River region, the shales are reduced in thickness to 500 feet, the Ogden 

 quartzite is absent by non-deposition, and the Mississippian limestone is 

 about 700 feet in thickness. This marked thinning of sediments east- 

 ward, by which the sedimentary section is reduced in thickness several 

 thousand feet, indicates an overlap upon a land-mass which, in central 

 Wyoming, brings the Permo-Carboniferous beds unconformably on the 

 Crystalline schists.* 



Unconpormities in the Uinta Eegion 



Powell recognized an unconformity at the top of the Uinta sandstone. 

 The overlying shales are said to fill hollows in the unevenly eroded sur- 

 face. This unconformity was not noted by the 40th Parallel geolo- 

 gists, and C. A. White (4, page 23), who was associated with Powell in 

 his later work in this region, has stated that the indications are so slight 

 as to be readily overlooked. No satisfactory evidences of such an uncon- 

 formity were found during the past field season. In every locality ex- 

 amined throughout the range the Lodore shales were found conformable 

 above and below with the associated strata, except in Duchesne and Rock 

 Creek canyons and in the vicinity of Green river, on the northern slope, 



* Darton : Personal communication. 



