560 REPORT UNITED STATES GEOLOGICAL SURVEY 



Triassic age, south of Station GO and its entire course is probably in rocks 

 of the same age. Near its mouth red sandstones outcrop, dipping at right 

 angles to the course of the river; i. e., to the northeast. North of this 

 stream two small and unimportant creeks flow into the Blackfoot. West 

 of it there are two more, one joining above the canon and the other below. 

 Then we reach the stream that comes from Station Go and flows south- 

 wardly into the Blackfoot, joining it opposite the northern end of Aspen 

 Eidge. The region between these two principal creeks is eroded into 

 ridges composed of Jura-Triassic and Carboniferous rocks, the continua- 

 tion of those between the southern branches of the river. Only two sta- 

 tions were made in this region, viz, Nos. 65 and 66. They were located on 

 the ridge south of John Gray's Lake. Station 65 is near the north end of 

 the ridge on limestones with a strike of south 33° east, dipping at an 

 angle of 55°. The strike curves to the eastward at the southern end of 

 the ridge, making an acute angle with the trend. Above the limestones 

 there are quartzites, and above the latter very dark blue limestones. The 

 lower limestones are probably the upper part of the Carboniferous. In 

 them at several places I noted the occurrence of oval concretion-like 

 masses arranged in concentric rings. I am inclined to regard them as 

 fossil remains rather than concretions, as I noticed a number of them 

 branching. They appear to cross the lines of s( ratification. 



The following general section was made in which the thicknesses are 

 only estimated : 



Section JVo. 19. 

 Base. Feet. 



1. Massive limestones outcropping on Station 65. Could not trace the beds 



below angle of dip 55° 400-j- 



2. White quartzite ) qqq 



3. Dark blue limestone J 



4 Reddish and greenish laminated sandstones 400 



5. Bluish-gray limestones 700 



6. Greenish and reddish sandstones and limestone shales alternating 850 



7. Limestones outcropping on Station 66 i 



8. Alternating limestones and shales outcropping in ridge running south > 1, 000+ 



from Station 66 ) 



Total * 4,150+ 



In stratum No. 5 the following fossils were obtained : ' 



Meelcoceras* gracilitatis, White. 

 Meelioceras mushbaclmnus, White. 

 Arcestes f cirratas, White. 

 Arcestes, two species. 

 Eumicrotis curta, Hall. 

 In No. 6 three or four undetermined conchifers and a new species of 

 Aviculopecten were found. 

 In No. 7 the following : 



Eumicrotis curta, Hall. 

 Aviculopecten idahoensis, Meek. 

 And in No. 8, near the top : 



Terebratula semi simplex. White. 

 Terebratula augusta, Hall. 

 Aviculopecten idahoensis, Meek. 

 Gervillia and undetermined conchifers. 



The discussion of the age of these beds is left to a future chapter. 

 The ridge presents the appearance of a monoclinal as do all the iso- 



- * The genus Meelcoceras is a new one established by Prof. A. Hyatt. (See Bulletin 

 U. S. Geol. Survey, vol. v, No. 1, 1879, p. 111.) 



