560 EEPOET UNITED STATES GEOLOGICAL SUEVEY 



Triassic age, south of Station 66 and its entire course is probably in rocks, 

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

 angles to tlie course of the river 5 i. e., to the northeast, i^orth 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 65 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 comx^osecl 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, i^os. 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 No. 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 5 



4 Eeddish and greenish laminated sandstones 400 



5. Bluish-gray limestones 700 



6. Greenish and reddish sandstones and limestone shales alternating 850 



7. Limestones outcroiDpiug on Station 66 ) 



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



from Station 66 ) 



Total 4,150-1- 



In stratum IsTo. 5 the following fossils were obtained : 

 Meelioceras* gracilitcUis, White. 

 Meekoceras omishhaclianus, White. 

 Arcestes f cirratus, White. 

 Arcestes, two species. 

 Eumicrotis curta. Hall. 

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

 Aviculopecten were found. 

 In No. 7 the following : 



JEumicrotis curta, Hall. 

 Aviculo]}ecten idahoensis, Meek. 

 And in No. 8, near the top : 



TerebraUda semisimplex, White. 

 Terebratula augusta, Hall. 

 Aviculoijecten idaJioensis, Meek. 

 Gervillia and undetermined concMfers. 



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 geuiis Meelcoceras is a new one established by Prof. A. Hyatt. (See BuUetia . 

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



