162 GEOLOGY OF THE BLACK HILLS. 



lied BeJjt. 



2. Gypsum, whitt' and auioiphous 3 



1. Red clays, and red sandy clays to base of bill . . 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 {ilO feet exposed). 



Feet. 



10. Clay, gray, white and i)nri)le ; cappinj; the bluff 35 



9. Sandstone, laineUar 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 — Bclemnites, Ammonites, etc 35 



7. Sandstone, white, massive and soft 20 



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



5. Sandstone, i)inkisli (the same as the summit of the last section) i)asses into 



Bed 4 00 



4. Sandstone, yellow and massive 90 



3. Sandstone, lamellar and white 10 



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



Red Beds. 

 1. Red sandy clays, with gypsum — 



In this section the cappmg 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 tliat 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 Fourclie Val- 

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

 described or identified — 



Ostrea strigilecuJa. Tancredia hulhosa. 



Camptonectes helUstriatus. Tancredia postica. 



Astarte fragUis. Dosinia Jurassica. 



Trapcz'tum BcJlcfonrchensis. Saxicava Jurassica. 



Tancredia inornata. Ammotiifes cordiformis 



Tancredia corhuliformis. Belemnites densus. 



