DETAILS OF THE JURA. 155 



The foothills on the west side of the east fork of the Beaver, for ten 



or fifteen miles north of Camp Jenney, reveal alon«^ their inner escarpment 



frequent exposures of the Jura, g"ivin<r an excellent idea of tlie structure of 



the formation; and in various places abundant and charactciistic fossils 



Were found. The valley is at bottom an undulating and somewhat rugged 



surface of the brick-red clays of the Red Beds, and these in places form 



the base of the foothills. Between them and the Cretaceous sandstone at 



the top of the cliff the gray clays and sandstones of the Jura crop out nt 



intervals. About ten miles north of Camp Jenney the following complete 



section was procured. 



Cretaceous {Ro. 1). 



Feet. 

 G. Sandstouo, white and massive, forming the summit of the clifiP. ... 85 



Jura. 

 5. Clays or marls, gray or greenish, witli a streak of red clay near the middle; 



in the upper part many belemnites 100 



4. Sandstones, white and shaly, in places somewhat massive, ripple-marked; con- 



tains fossils near its base {Grypluca calceola, etc.) 50 



3. Clays or marls, brown or gray, with some gypsum ; about 10 feet from base, 



in a thin and impure limestone, werefound a Grypha^a and ammonite frag- 

 ments 70 



Red Beds. 



2. Gypsum, white, amorphous - 8 



1. Red clay to bottom of creek . . 130 



The following section was measured near Camp Jenney, on the north- 

 ern side of the pass which Beaver Creek has opened through the foothills. 



Cretaceous {Xo. 1). 



Feet. 



C. Sandstone, yellow and white, somewhat lamellar, and containing ripple-marked 



surfaces 60 



5. Sandstone, yellowish with red stains, heavily bedded 40 



4. Sandstone, veiy white, fine-grained and massive, easily decomposing into fine 



white sand ; forms a well-marked clifl", eaten iuto caverns and holes 100 



tTwra, 



3. Covered by talus and not well exposed ; at intervals outcrops of gray or green- 



ish clays or marls, with occasional bands of limestone containing fossils ; 



also outcrops of sandstone 70 



2. Marls or clays, gray and piuple, with nodules of impure limestone ; base 



covered 110 



1. Marls or clays, gray andpuriDle, with thin bands of impure limestone, coutain- 



iug fossils to base of cliff. . 20 



