GEOLOGICAL REPORT. 275 



however, be necessaiy to wait until more complete collections of fossils and accurate 

 sections of the strata can be procured. 



All the Jurassic fossils which I obtained in this section of the country were found 

 on North Platte River, close below the Red Buttes, within a few feet of each other. 

 in some strata highly charged with organic remains, and which reach the surface at 

 the lowest central point of an anticlinal exposure. A combination of local upheavals, 

 which cause abrupt changes of the dip, both in direction and degree, and the discon- 

 nection of the exposures, prevented me from obtaining a complete section, and from 

 tracing the limits between the Jurassic and older formations; while the overlying 

 strata, at a greater distance from the axis of elevation, have such a slight dip, and are 

 mostly covered over so much with soil and detritus that their succession and relative 

 superposition are not perfectly plain. The difficulty is increased by the scarcity of 

 fossils, of which I did not notice any between the point mentioned and a locality 7 

 miles lower down the river. The succession of the strata along the river, as far it 

 could be observed, is the following, beginning about 7 miles below the hed Buttes: 



1. Dark gray and blue argillaceous slates and marls, with harder seams and con- 

 cretions of argillo-ealeareons marl, the latter mostly inclosing fossils, (hfrca coHf/csta, 

 I><u:idtti'.% and a fine new Inoceramus, of great size, /. Simpsoni Meek. Fissures of the 

 rock are thickly coated with slender silky crystals of gypsum. These beds, forming 

 an exposure of about 70 feet thickness, evidently correspond to No. Ill of 

 the Nebraska Cretaceous section of Messrs. Meek and Ilayden, and appeared to be 

 horizontal. 



2. A gap probably corresponding to more clays and marls. 



3. Sandstones, heavy-bedded, light-colored or brown, and ferruginous, passing 

 down into thinly stratified, partly shaly sandstones, ami still lower into brown and 



.gray arenaceous shales, with some seams of sandstone. The observed thickness 

 exceeds 100 feet, and may be much greater. The dip is very slight to the east. 

 These sandstones closely resemble those of the Lignite formations, as well higher up 

 as lower down on Platte River. I did not notice with them any beds of coal, but 

 numerous imperfect marks of fossil plants. 



4. A great thickness of sandstones, like the upper ones, of No. 3. Underlying 

 them conformably, there are— 



5. Dark bluish-gray, apparently altered shales and slates, with irregular seams 

 and concretionary masses of black limestone, which have an even fracture and are 

 hard and very brittle, as if they had passed through a kiln. Seventy feet or more. 



6. A remarkable bed, 6 feet thick, of a light greenish-yellow argillaceous sub- 

 stance, which is unctuous to the touch, and readily imbibes water, which renders it 

 hio-hlv plastic. It contains gypsum in single crystals and alkaline salts. 



7. Over 150 feet more of the dark shales and slates, like 5, with efflorescences of 

 gypsum on the fissures. 



8. Sandstones, conformably underlying the shales, of considerable thickness. 



9. Shales and slates, dark bluish-black, or light-colored, variegated gray, red, 

 green, &c. About 100 feet. 



10. Some beds of brown and gray sandstone, partly slaty, laminated, and calca- 



