196 GEOLOGICAL SUEVEY OF THE TEKRITORIES. 



from tlie lithological identity with beds that are undoubtedly Jurassic in 

 the following section made by Dr. Hayden at Box Elder, in 18G9. The 

 following is the section made by him in ascending order :* 



1. Brick red sandstone, with irregular laminse, and all the usual signs of 

 currents or shallow water. Some of the layers loosely laminated, 

 causing projections. Thickness, 300 feet to 400 feet. 



2. Yellow or reddish yellow massive sandstone, 60 feet. 



3. Grayish yellow, rather massive sandstone, 50 feet. 



4. Ashen brown nodular, or indurated clay, with deep, dull purple 

 bands ; with some layers of brown and yellow fine-grained sandstone, 

 undoubtedly the usual Jurassic beds, with all the lithological characters 

 as seen near Lake Como, on the Union Pacific llailroad. Near the 

 base of these beds are thin layers of a fine-grained grayish calcareous 

 sandstone, with a species of Ostrca and fragments of Pentacrinus 

 astericus. Scattered through this bed are layers or nodules of impure 

 limestone, 150 feet to 200 feet. 



5. Sandstone and laminated arenaceous material varying in color from 

 dirty brown to grayish white, with layers of fine grayish-white sand- 

 stone, 200 feet. 



Dr. Hayden says, " I do not hesitate to regard the beds described as 

 4 and 5 as of Jurassic age, and they are better shown here than at any 

 other point between Fort Laramie and tbe south line of Colorado, on 

 the eastern sloi^e of the Eocky Moontains." Nos. 1, 2, and 3 of this 

 section correspond to Nos. 16 to 14 of the South Platte section, (No. 1.) 

 Beds ISTos. 4, 5, 6, and 7 of section No. 1 form tbe main hog-back which 

 is so conspicuous along the entire extent of the foot-hills. No. 4 forms 

 the summit of the hog-back, and is a rather fine-grained uniform 

 textured siliceous sandstone. All these beds belong to the Dakota 

 group No. 1 Cretaceous. Layer No. 5 contains a large percentage of 

 carbonaceous material, and in it I found fragments of leaves and stems. 

 Among the former. Professor Lesquereux has recognized a Froteoides 

 very near Froteoides acuta, (Heer.) These shaly sandstones weather of a 

 bluish color in places, and are followed by No. 6, which passes into No. 

 7. The latter has occasional shaly bands, and in some places instead 

 of being yellow the sandstone becomes reddish. Space No. 3 is filled 

 in with No. 2 Cretaceous, Fort Benton group, and perhaps a portion of 

 No. 3 Niobrara division, to which formation also I refer the layers marked 

 Nos. 1 and 2. No. 2 is somewhat sandy, and in places is very dark 

 colored, and on being fractured has a perceptible bituminous odor. It 

 contains quantities of Ostrea and a few Inoceranii. East of these beds 

 the country is so leveled that the remainder of the Cretaceous forma- 

 tion and the entire extent of the Tertiary beds are concealed, being- 

 covered by the local drift froDi tbe hills. That the Tertiary layers are 

 not far distant, however, is evident, for along the Platte Eiver are ex- 

 posures of lignitic sandstones. After passing out through the main 

 hog-back, (Cretaceous No. 1,) the Platte turns to the northward, and its 

 course is about north 7° east. The dip of the main hog-back at the 

 Platte Eiver is north 65° east ; angle 55° to 60°. Fig. 2, Plate I, repre- 

 sents a section made at Willow Creek, five miles south of the Platte. 

 The dip here is north 55° east ; angle of inclination, 50° at the outside, 

 increasing to 55° as we go down to the red-beds. It is not necessary to 

 give the beds of the section here, as it would be a repetition of the order 

 given in the Platte section, (No. 1.) They are so much alike that I will 

 refer only to those where there has been some change. The thicknesses 

 are about the same. In No. 14 of the Platte section, at this place, we have 



* Eeport for 1869, page 19. 



