pbale.1 GEOLOGY SECTIONS OF JURASSIC EAGLE RIVER, &C. 125 



No. 7. — Section of Jurassic, head of second canon, Eagle River, south side. 



Top. Thickness in feet. 



1. Space probably rilled with sandstones and marls, about , 500 



2. Laminated sandstones and blue limestone ) ,qq 



3. Light-yellowish brown sandstone 3 



4. Blue limestone 50 



5. Gray shaly sandstones with interlaminated marls and thin bands of blue lime- 



stone 200 



Base. 



Total about 940 



A portion of these bids may be Cretaceous. 



Nowhere along the coarse of the Eagle, nor at any point in the dis- 

 trict, does the Jurassic formation occupy any extensive area. It occurs 

 only as a narrow belt outcropping beneath the Dakota group. It is, 

 therefore, shown principally along the courses of the streams. 



The line of outcrop on which the section given above was made con- 

 tinues conformable with the Cretaceous and Triassic strata, following 

 the curve indicated on the map, and crosses to the north side of the 

 Eagle at the lower end of the canon. 



Around the almost circular area of Cretaceous rocks south of the 

 Eagle, represented on the map, there is, in all probability, a narrow belt 

 of Jurassic, although I cannot be positive, as I have not followed it 

 around, and judge so only from my observations from stations 6 and 8. 

 With this exception, I believe there are no Jurassic strata exposed be- 

 tween the Eagle and Frying-Pan Creek. In the low, rounded hills 

 which occupy the greater portion of this space, all the beds above the 

 Triassic sandstones have been removed. 



Grand River. — From the mouth of the Eagle to the mouth of Roaring 

 Fork there are no exposures of Jurassic age close to the Grand. The 

 Red Beds here form the top of the stratified rocks and are covered with 

 a volcanic layer. There may be an occasional outcrop between the 

 head of a creek of Grand River and Roaring Fork. If so, they must be 

 very limited in extent. At the head of Mesa Creek, a branch of Roar- 

 ing Fork, there is probably a narrow belt dipping to the south or south- 

 east. 



In the hog-backs, on the west side of Roaring Fork, the Jurassic 

 strata are seen following the line of the overlying and underlying strata, 

 disappearing beneath the volcanic rock capping the hills, and re-appear- 

 ing on the Grand below the mouth of Roaring Fork, finally crossing 

 the Grand, aud. extending to the northwest, forming a portion of the 

 hog-back range, that dies away in the plateau. Between this point and 

 the mouth of the Gunnison there are no other exposures of Jurassic 

 age along the course of the Grand. 



No. 8. — Section of Jurassic, west side of Roaring Forlt, below station No. 14. 



Base. Thickness in feet. 



1. Coarse gray sandstone 20 to 30 



2. Space probably filled with sandstones and shales 20 



3. Fine-textured light-yellowish sandstones 15 



4. Space probably filled with sandstones, marls, and shales, and perhaps some 



limestones 165 



5. Light-colored fine-grained siliceous sandstone 30 



6. Soft shaly sandstone, probably slightly argillaceous 12 



7. Blue limestone 8 



8. Gray sandsto nes, becoming greenish near the upper part 125 



9. Dark-brownish gray sandstone, becoming lighter as we ascend 15 



10 Brownish sandstone with interlaminated black shales 20 



Top. 



Total about 440 



