PERMIAN PERMO-CARBONIFBROUS 



439 



(south) side of the range the formation is well exposed in all the prin- 

 cipal canyons from the Provo river to Green river. This formation, like 

 the "Uinta," is quartzitic in the western and central parts of the range 

 and grades into a rather soft sandstone in the eastern part. No fossils 

 were found in the Weber formation. 



Permian Permo-Carhoniferous—l^omencMuTe and correlation.— The 

 Permd-Carboniferous series of the Uinta range seems to correspond in 

 position, thickness, and general lithologic characters to the Upper Coal 

 Measure and Permo-Carboniferous formations of the 40th Parallel Sur- 

 vey. On similar grounds they may be correlated with the Aubrey lime- 

 stone of Walcott's Grand Canyon section. The correlation with Powell's 

 section is less definite. The limestones overlying the Yampa sandstone 

 of the Upper Aubrey group and an undetermined thickness of the shales 

 and soft sandstones of the Shinarump group appear to correspond to the 

 beds under discussion. 



Description. — The upper beds of the Weber formation are calcareous 

 sandstones and siliceous limestones which weather yellow and grade into 

 the thin red shales and red and blue limestones of the upper part of the 

 Permo-Carboniferous series. This series is well exposed on the Duchesne 

 river, Eock creek, Whiterocks creek on the south side of the range, and in 

 Horseshoe canyon of Green river on the north side of the range. 



One of the best sections occurs on the east side of Duchesne river below 

 the mouth of West fork. There the lower 600 feet of the Permo-Car- 

 boniferous are formed of the red and purple shales and blue limestones. 

 Above is 1,000 feet of light gray and white sandstones, with some inter- 

 bedded limestones in the lower part. In the upper part these sandstones 

 occur in alternating layers of soft and compact beds full of peculiar black 

 points or specks. These are succeeded by 800 to 900 feet of red shales, 

 with a prominent band of light-colored shale at the top. 



POST-PALEOZOIC 



Trias. — The Trias was defined by Emmons (2, page 200) as consisting 

 of red sandstones with a series of clayey beds at the base, having an esti- 

 mated thickness of 2,500 feet. Powell (1, pages 150-153) did not sepa- 

 rate the Jura from the Trias. He divided the Jura-Trias beds into the 

 Shinarump, A^ermilion Cliff, White Cliff, and Flaming Gorge groups, 

 having a total thickness of 3,845 feet. The Trias of the 40th Parallel 

 Survey appears to correspond to the Shinarump, Vermilion Cliff, and 

 White Cliff groups of Powell. The writer has classed the shales at the 

 base of the Trias with the Permo-Carboniferous. The line of division 

 between the Trias and the Permian is placed at the base of the massive 

 cross-bedded sandstones. 



