124 GEOLOGICAL SURVEY OF THE TERRITORIES. 



» 



sen ted in Fig. 2. Farther on this fold probably becomes a fault. In the 

 two figures just referred to, the red sandstones are represented at a. 



To the west and southwest of the Gunnison the red sandstones seem 

 to prevail extensively, and x>robably from the top of the plateau which, 

 as seeu from the Gunnison, extends in this direction. The Indians give 

 the lower canon of the Gunnison the name of Unaweep or Eed Earth, 

 evidently on account of the exposures of Eed Beds along the edge of the 

 river. 



JURASSIC. 



Immediately above the Eed Beds, between them and the Dakota group, 

 is a series of sandstones, marls, and limestones which I have referred to 

 the Jurassic, although I was unable to find any fossils at any point 

 where they were exposed in our district of 1874. 



They correspond lithologically and stratigraphically to the strata that 

 in 1873 I referred to that horizon. The reasons for so doing were stated 

 in the report for 1873, and I will not take up the space here with the 

 repetition of them. They are generally in thin beds, the sbaly element 

 predominating. Their softness has rendered them readily amenable to 

 eroding influences, so that they are generally covered with debris, and 

 it is difficult to make complete sections of the formation. 



The Jurassic formation is widely spread in the Eocky Mountains, its 

 distribution being identical with that of the Dakota group and the un- 

 derlying Eed Beds. Hay den, Newbery, Comstock, and others have 

 recognized it in various portions of the West. Marcou* also claims to 

 have discovered it in New Mexico and other parts of the West, but, as I 

 shall subsequently point out, the layers referred by him to this horizon 

 are probably of Cretaceous age, while those that are Jurassic he refers 

 to the upper part of the Triassic. 



Dr. Hay dent, speaking of the formation, says: "At both of these 

 localities (near the Wind River Valley and Big Jlorn Mountains), at the 

 Black Hills and at the Eed Butte on the North Platte, as well as at 

 the other localities already mentioned in Utah (near Uintah and Weber 

 Rivers), the rocks containing these Jurassic fossils consist of a series of 

 grayish, ash-colored and red argillo-calcareous, more or less gritty 

 strata, with beds of soft dark-brown and reddish sandstones. These 

 beds preserve a remarkable uniformity of character taken as a group, 

 wherever they have been seen, and need never be confounded with the 

 Cretaceous or Tertiary rocks so widely distributed over the Northwest- 

 ern Territories, even where no fossils are to be found." 



In Colorado, Dr. Sayden, Mr. Marvine, Dr. Endlich, and myself found 

 the Jurassic layers presenting the same general characters that they do 

 north of the Uuion Pacific Eailroad. Along the eastern edge of the 

 mountains in Colorado, the greatest thickness measured was 870 feet. 



Eagle River. — On the south side of the river no strata of Jurassic 

 age appear until we reach the head of the second canon, when it crosses 

 from Mr. Marvine's district conformable with the overlying Cretaceous, 

 and underlying Triassic. 



The following is a section made on the south side of the river at the 

 point where the section previously given of the Triassic sandstones 

 was made. 



*Geology of North America, by Jules Marcou. 



t Geological Report of Exploration of the Yellowstone and Missouri Rivers. F. V. 

 Hayden, under Capt. W. F. Rayuolds, 185 l J-'60. 



