162 GEOLOGY OF THE BLACK HILLS. 



Bed Beds. 



2. Gypsum, white and amorphous 3 



1. Red clays, and red sandy clays to base of hill. . 50 



This section represents only the lower portion of the Jura. In the 

 following section, observed by Mr. W. F. Patrick two miles farther west, 

 the upper portion is better represented: 



Jura (410 feet exposed). 



Feet. 



10. Clay, gray, white and purple ; capping the bluff 35 



9. Sandstone, lamellar and yellow ; upper layers hard and brown 30 



8. Sands, argillaceous, yellow and greenish, with layers of a calcareous sand- 

 stone full of fossil mollusks — Belemnites, Ammonites, etc .... 35 



7. Sandstone, white, massive and soft 20 



6. Sands or sandy marls, white and calcareous, with Belemnites 80 



5. Sandstone, piukish (the same as the summit of the last section) passes into 



Bed 4 60 



4. Sandstone, yellow and massive . . 90 



3. Sandstone, lamellar and white 10 



2. Clay, white and gray, with sandy clays 50 



Bed Beds. 

 1. Red sandy clays, with gypsum — 



In this section the capping- Dakota sandstone is wanting, but appears 

 some distance down the northern slope of the foothills. The clay at the 

 summit of the section is shown by a comparison with other sections to be 

 very nearly the extreme upper portion of the Jura, so that the total of 410 

 feet represents very closely the full force of the formation at this point. 

 The bed numbered 8, about 350 feet above the Red Beds, is a marked 

 fossil-bearing horizon of the Jura in the Redwater and Belle Fourche Val- 

 leys ; it has yielded a large collection, in which Professor Whitfield has 

 described or identified — 



Ostrea strigilecula. Tancredia bulbosa. 



Camptonectes bellistriatus. Tancredia postica. 



Astarte fragilis. Dosinia Jurassica. 



Trapezium Belief our cliensis. Saxicava Jurassica. 



Tancredia inornata. Ammonites cordiformis 



Tancredia corf) id if or mis. Belemnites densus. 



