PRE-CAMBRIAN FORMATION 435 



The character of the rocks and the stratigraphic position and thickness 

 of the qnartzite series suggest that it is to be correlated with the great 

 quartzite sections of the Wasatch and other ranges of Utah and eastern 

 Nevada whose position beneath the Olenellus shales of the lower Cam- 

 brian is generally recognized. No fossils whose stratigraphic position is 

 known have been found in this formation. The oldest fossils are of 

 Lower Mississippian age, but are separated from the "Uinta" quartzite by 

 500 to 1,200 feet of shales. While the correlation seems to rest on in- 

 conclusive evidence, it should be remembered that there is no other known 

 series of such extent and thickness with which it can be correlated. 



Description. — This formation constitutes the broad top of the range. 

 At the eastern end the folding is less pronounced and the overlying 

 Mississippian limestones form the surface rocks. At the western end the 

 formation is covered by lava flows in Kamas valley, but is again exposed 

 on the western slope of the Wasatch range. The base of the formation is 

 not exposed, but its thickness exceeds 12,000 feet. In the western part of 

 the range, especially on the northern flank, the strata are very compact, 

 dense quartzites. In other parts there are all gradations to a soft sand- 

 stone. The prevailing color is reddish brown, with a considerable thick- 

 ness of purple quartzites about the middle of the formation. The upper 

 part contains striped quartzites, and in both eastern and western parts of 

 the range there are several bands of interbedded conglomerates with 

 greenish sandstones at the top. In some areas white quartzites are well 

 developed, particularly in the Green Eiver region. One of the most 

 favorable localities for the study of this formation is along the east side 

 of the East fork of Smiths fork of Green river, on the north side of the 

 range. The beds dip 25 to 40 degrees to the north, and are exposed in 

 continuous section to and including the Lodore shales about one mile 

 above China lake. 



CAMBRIAN LODORE SHALES 



Nomenclature and correlation. — In Lodore canyon of Green river 

 Powell noted the occurrence of 500 feet of shales between the "Uinta" 

 sandstone and the Aubrey limestone, and designated them Lodore shales. 

 He correlated them with the Tonto shales of the Grand Canyon region, 

 and stated that Carboniferous fossils had been found in them. The 

 names of the species or locality where found are not given, and there is 

 considerable doubt as to the accuracy of this statement. Walcott con- 

 siders that the Tonto shales are of middle and upper Cambrian age. In 

 my reconnaissance no fossils were found, although considerable time was 

 devoted to searching for them at numerous localities where the shales 



