130 GEOLOGICAL SURVEY OF THE TERRITORIES. 



The lower portion of this section is probably Jurassic. 



The area of ('retaceous represented on the map lying between the 

 semicircular ridge and g creek is probably almost entirely of the sand- 

 stones of the Dakota group. There may be some of the layers of No. 

 2 and No. Sin places, as shown in Pig, 1, Plate I. There are no other 

 outcrops of No. 1 on Eagle Eiver or its tributaries within the limits of 

 our district. 



Grand River. — Between the Grand and Eoaring Fork, at the head of 

 Mesa Creek, there are, judging from the view we had from station No. 11, 

 outcrops of the Dakota group dipping to the southwest. It also out- 

 crops beneath the mesa between this creek and Frying-Pan Creek, near 

 the base, on the south side. Between the Grand and Eoaring Fork 

 there may be a few patches of Cretaceous, but, if so, I think they are of 

 higher beds than the Dakota group. On the west side of Eoaring Fork 

 it forms the summit of the prominent hog-back ridge. On station 14 it 

 is a massive light grayish siliceous sandstone, the outcrop of which 

 measures 63 feet. If the beds marked 8, 9, and 10, in the section of the 

 Jurassic (section No. 8) made here, are included, the following would be 

 the section of the Dakota group at this point. 



No. 10, — Section on Station No. 14. 



Top. Thickness in feet. 



1. Massive grayish white siliceous sandstone 63 



2. Brown sandstone, with fine black shales ^ 20 



3. Dark brownish-gray sandstone, becoming light-colored near the top 15 



4. Light greenish sandstone 125 



Base. 



Total, about 203 



The character of these beds, I think, warrants their being considered 

 Cretaceous rather than Jurassic. The black shales in No. 2 probably 

 occupy the same horizon that in the other places is filled with the lignitic 

 beds. If they are not considered Cretaceous we have only a thickness 

 of 03 feet for the Dakota group. Above the layer marked No. 1 the 

 beds have been eroded and covered with the debris, leaving a valley 

 between the hog back and the hills to the west. On the Grand, below 

 the mouth of Eoaring Fork, the Dakota group comes out from beneath 

 the volcanic rock of station 16. At station 14 the strike of the hog- 

 backs is north 15° west, and the angle of dip 30°. Station 17 was on the 

 sandstones of the Dakota group. The inclination here is 35°. This 

 seems to increase to 50° or 60° to the westward. The strike is north 75° 

 to 80° west. The hog-backs extend about seven miles beyond station 

 17, when they cross the river into Mr, Marvine's district, and the Grand, 

 from that point to the mouth of the Gunnison, flows through beds of 

 higher horizons, not reaching the No. 1 until the river is joined by the 

 Gunnison. Here it outcrops in the bluffs. I will reserve the description 

 to the section devoted to the Gunnison. 



Gunnison River. — At several points bordering the meadow-like expan- 

 sions of the valley of the Gunnison below the mouth of Cochetopa Creek, 

 there are indistinct outcrops of sandstones that probably represent a 

 portion of the Dakota group. As we proceed down the river these out- 

 crops becomemore distinct, and below station 73, besides the No. 1, shales 

 of No. 2 are represented, showii at c in Fig. 1, Plate XIV. The Cretaceous 

 rocks seem to have been subjected to considerable erosion, i)receding the 

 lava flow that has covered them. This is shown by the change in the 

 strata shown in the figures in Plate XIV, which are sections on the north 



