156 GEOLOGICAL SURVEY OF THE TERRITORIES. 



TERTIARY BETWEEN GRAND AND GUNNISON RIVERS. 



The only portion of the district in which Tertiary rocks are seen is 

 in the region between its two main streams. I have no absolute proof 

 that the Lignitic group is present. At all the localities I visited, the 

 intermediate bed^ from the upper part of the Fox Hills beds to the 

 red sandstone bed that 1 took as the base of the Green Eiver and 

 Bridger series were covered. The Lignitic group may include a portion 

 of the beds above and a part beneath. It is impossible to define any 

 line of separation. Although I could see no uncouformability between 

 the Cretaceous and overlying Tertiaries, it is probable that in other 

 places evidences will be found, especially on the edges of the Tertiary 

 basin. In a conglomeritic sandstone on Plateau Greek I found an 

 inner convolution of a ScapMte. It was a pebble, and proves that the 

 layer in which it was found, is of Post- Cretaceous age, its materials com- 

 ing from the disintegration of Cretaceous rock which were above water- 

 level when the stratum was deposited. 



GREEN RIVER AND BRIDGER GROUPS. 



I shall use the name Green Eiver group to include also the Wah'satch 

 group of Hayden. Cope restricts the name to the Green Eiver shales. 

 Whether we call them Eocene or Miocene depends upon the view we 

 take of the beds below. The vertebrate palentologists consider them 

 Eocene, while all who hold to the Tertiary age of the Lignitic group 

 place them in the Miocene. 



As has already been stated, the greater portion of the Tertiary beds 

 exposed in the district is referable to the Green Eiver and Bridger 

 groups. These strata are seen between the Grand and Gunnison rivers, 

 west of Eoaring Fork, and are almost horizontal, dipping slightly to the 

 eastward beneath the basaltic-capped plateaus, which are fully described 

 in other portions of the report. The area is shown on map E. 



The characters of the included rocks will be given as we proceed. 

 The best exposures are seen on Plateau Creek, a branch of the Grand 

 Eiver, which joins it some distance above the mouth of the Gunnison, 

 after cutting deeply into the strata. The following section will give the 

 best idea of the succession of the strata on Plateau Creek. 



No. 19. — Section of Tertiary Beds. — Plateau CreeTc. 



Thickness 

 Base. Ft. In. 



1. Red sandstone ^ 



2. Yellow and white sandstones 



3. Red sandstone, 30 feet 



4 Variegated red, yellow, and bluish marls, sandstones, and clays.. 



5. Bluish and black argillaceous beds 



6. Yellow sandstone 



7. Black argillaceous beds 



8. Brownish red sandstone }2, 000 



9. Soft greenish argillaceous shales 



10. Green sandstone shales 



11. Black argillaceous shales - 



12. Massive sands'tones in pinkish-white and yellowish-gray layers, 



with interlaminated greenish shales. Some of the layers are )-250 

 conglomeritic 1 



13. Dark greenish shaly sandstone ^ 



14. Series of soft variegated beds, yellow, reddish, and black, much like those 



given in lower part of this section. They are generally concealed, but 

 where exposed the debris, from the softness of the strata, makes it 

 almost impossible to get the section in detail. Thickness about 740 



