DETAILS OF THE JUKA 161 



the Red Valley, the sole representatives of the former wide-spread distribu- 

 tion of those formations. Oi' this clmracter is the butte near Spearfish, a 

 section of which has already been given. 



On the east side of Si)earfish Creek, some two or three miles noi-th of 

 the section last given, the folhnving measurements were made by Mr. Jen- 

 ney on the escarpment of the foothills. 



Cretaceous. 



Feet. 



9. Sandstone, massive, yellow ; the Dakota sandstone ^ 75 



Jura (3i0 feet). 



8. Unexposed 50 



7. Saiids and sandy shales, with a few fossils near the top IL'O 



0. Sandstone, soft, cinud)linj^ and pinkish ; weatht-rin^;- to a loose reddish sand. 00 

 5. Sandstone, massive, yellow and pink; laminated with layers of diflt'erent 



shades of red ; containing a few star-fish impressions 40 



4. Sand, yellow 70 



Fed Beds {exposed 24:5 feet). 



3. Gypsum, white, amorphous .... 10 



2. Sandstones and sandy clays, deep red ; ^vith gypsum 220 



1. Limestone, pink 25 



The " sands" mentioned in this and the following sections are fine and 

 light colored, produced probably by the decomposition of a friable sandstone, 

 but a little digging into the outcrop failed to discover a coherent rock. 



Westward along the foothills on the north side of the Redwater the 

 Jura is shown by frequent exposures to occupy the greater j)ortion of the 

 height of the cliffs, though the red clays encroach more or less upon their 

 lower part, while the summits are usually capped by the Dakota sand- 

 stone. The dip of the strata is slight, commonly only 5*^ or 10°, and in 

 direction a little east of north. About ten miles west of the junction of 

 Redwater and Spearfish Creeks (forming the Deepwater) the following 

 section w^as obtained by Mr. Jenney: 



Jura. 



Feet. 



7. Sandstones, soft, pink, decomposing to a reddish sand 60 



G. Sandstone, massive, soft, yellow 90 



5. Shaly sandstones, yellow in color, containing a few casts of moUusks 20 



4. Sandstone, lamellar, white and crumbling 10 



3. Clays or mails, white and gray, full of Belemnites in the upper portion 70 



11 B H 



