622 REPORT UNITED STATES GEOLOGICAL SURVEY. 



Jura-Trias, making- the divison of the formations in the .section partly on 

 lithological grounds. 



JURA-TRIAS. 



Immediately overlying the Carboniferous limestones in the Salt River 

 Range, and in the ridge of Station 00, is a series of alternating arena- 

 ceous beds and laminated limestones. They are conformable to the < !ar- 

 boniferous, and, at first, were referred to the Permian division of that 

 age, as above them was a series of red sandstones and shales, which 

 were without hesitation referred to the Trias. The examination of their 

 organic contents, however, by Dr. White indicates them to be of Triassic 

 age. With these are Jurassic forms. Above the red sandstones are 

 blue limestones, followed by shales and quartzites, in which undoubted 

 Jurassic fossils are numerous. The paleontological question suggested 

 by the mingling of Jurassic and Triassic forms will be discussed else- 

 where by Dr. White. 



Triassic. — The red sandstones and the beds lying between them and 

 the Carboniferous limestones I shall treat under this head, dividing them 

 into the two groups, which I call the "Red Beds" and the "Meekoceras 

 Beds"; the latter is named from the characteristic fossils, a new genus, 

 of which three species were collected. 



The Triassic rocks are found entering conformably into the folds which 

 have resulted in the formation of the various ranges of our district. I 

 shall now briefly recapitulate the principal occurrences of the rocks. 



Green River Basin. — On the west edge of the Green River Basin the 

 fold that marks its western boundary is rarely cut through so as to 

 expose the Trias. At Fontenelle Canon, below the Jurassic beds, red 

 quartzites outcrop. These were referred to the Red Beds, as was also 

 the outcrop of red sandstones at the mouth of the canon of Ham's Fork 

 (p. 534.) Farther north a quartzite referred doubtfully to the Trias is 

 occasionally seen in some of the canons cut by the streams on their way 

 from Meridianal Valley to the Green River Basin. All these outcrops 

 are limited. • 



Wyoming Range. — On the summit of the Wyoming Range an area of 

 Red Beds occupies the synclinal depression which extends northward 

 from Station 55. At the latter point was made the only detailed section 

 of the Red Beds. It is given in Section ~No. 10, and shows them to con- 

 sist mainly of dark red quartzites, with shaly and calcareous layers 

 coming in towards the base. The total thickness here is a thousand feet 

 or more. The u Meekoceras Beds" probably show below, but the section 

 could not be carried through them. 



Along the western side of the range the " Red Beds" show in the valley 

 of John Day's River, forming low hogbacks. The Triassic rocks of the 

 Wyoming Range are probably the northern continuation of those seen in 

 Fontenelle Canon. The greater elevation here and the consequent ero- 

 sion have removed the overlying Jurassic, which in Meridian Ridge con- 

 ceals the Trias. 



Salt River Range. — In the Salt River Range we find both groups of 

 the Trias entering into the complicated folds which enter into its struct- 

 ure. The outcrops of Triassic do not appear to extend north of Glacier 

 Creek, and for the details of their occurrence in the region of Stations 50 

 and 58, the reader will have to refer to the description of the Salt River 

 Range given in Chapter IY. At Station 50, above the Carboniferous 

 limestones containing Productus mitltistriatus, is a series of arenaceous 

 and calcareous beds, which, when first seen, were referred to the upper 

 division of the Carboniferous. They contained a few fossils, which have 



