GEOLOGY OF THK REGION 297 



The Wasatch limestone has shrunk to about 1,000 feet of buff, cherty, 

 calcareous beds, alternating in the upper part with white sandstones. 

 Although the limestones are always light colored, they often present a red 

 or striped appearance in cliff exposures, and thus resemble rocks of the 

 same horizon in the Grand canyon of the Colorado, where they are stained 

 by waters seeping down over their face from red shales above, and were 

 hence called by Powell the Eed Wall limestones. They carry Pennsyl- 

 vanian fossils in the upper part, and iVIississippian in the lower. 



Beneath these are quartzites with interbedded conglomerates and sandy 

 shales, generally white or greenish, often red by oxidation, which are in 

 extremely variable thickness, reaching a maximum in the Duchesne val- 

 ley of 1,100 feet. Mr Berkey's surmise that these correspond to the 

 Ogden quartzite (now considered Ordovician), though as yet unsupported 

 by paleontologic evidence, is considered a probable assumption, and the 

 name has been provisorily retained. If there be an unconformity by 

 erosion, it would be most naturally placed between this and the Shale 

 series below, because of the variation in thickness of this siliceous mem- 

 ber, it being entirely wanting on the northern flanks of the range ; but no 

 direct evidence of erosion could be detected and the conglomerate has not 

 the characteristics of a true basal conglomerate. 



In the Duchesne valley the Shale series consists of about 1,200 feet of 

 thin-bedded, dark, argillaceous shales, in which we were unable to detect 

 the pyrites to which Mr Berkey refers. Their best exposures are in Hades 

 Creek and Iron Creek ravines, adjoining the fault. They have no rela- 

 tion, as the latter name might suggest, to the deposits of iron ore which 

 occur, as Mr Boutwell has noted, in the Wasatch limestones much higher 

 in the geological column. 



The thickness of the Shale series is also variable, being nowhere so 

 great as in the Duchesne valley; but it is never entirely wanting, as is at 

 times the Ogden quartzite. In my original field notes I find mention of 

 a few hundred feet of greenish shales observed at various points, sup- 

 posed to be part of the upper members of the Uinta quartzite. 



The Iron Creek fault has not the structural significance that Mr Ber- 

 key would assign to it. It can only be traced 7 or 8 miles on either side 

 of the Duchesne valley, though similar strike faults occur at various 

 points along the southern flanks of the range, more frequently where the 

 strata have taken a sudden downward bend, so that the existence of the 

 fault is less evident than on the Duchesne. In spite of its striking prom- 

 inence in the valley bottom, the Iron Creek fault could not be detected on 

 the plateau-like summit of the spurs on either side of the Duchesne, un- 

 less one knew of its existence and made a special search for it ; for on the 



