154 GEOLOGY OF THE BLACK HILLS. 



fully ripple-marked — an evidence of the shallowness of the water in which 

 they were laid down. 



The clays or marls do not appear to be more particularly confined 

 to one part than another, though they perhaps are not so strongly 

 developed in the extreme upper portion as in the lower two-thirds of the 

 formation. Their colors are gray or drab and dull green, with an occa- 

 sional streak of bright red or pink. They often contain seams of limestone 

 more Or less impure, and these are possibly more common in the lower 

 portion of the formation. The limestones are frequently fossiliferous, but 

 seem never to be more than a few inches in thickness, and do not constitute, 

 so far as could be determined, continuous strata. 



Everywhere a large proportion of the formation is composed of sand- 

 stones, which are usually light in color and even sometimes of a snowy 

 whiteness. As a rule they are very soft or shaly, passing into sandy 

 shales. Soft incoherent sands are met with at different points on the Red- 

 water, which are probably the result either of the decomposition of soft fine 

 sandstone or of the leeching of sandy clays. 



Along the Redwater Valley, from Warren Peaks eastward to the 

 Spearfish, there were found two horizons yielding fossils in abundance; 

 one at 135 feet and the other at 350 feet above the Red Beds. The latter 

 horizon is also well marked near Bear Lodge, but was not recognized 

 elsewhere. 



The meagerness and indefiniteness of this general description is due 

 in part to the variability of the strata, and in part to the imperfection of 

 the observations. The center of interest in the Hills was in the main body 

 of the uplift, and what was learned of the periphery was acquired by radial 

 excursions along the creek valleys. The Jura was crossed at a number of 

 points, but it was not followed on its line of outcrop. Each observation is 

 therefore isolated, and it will probably be best to put each one on record by 

 itself. In the pages immediately following, the observed sections will be 

 described in order, beginning with the point on Beaver Creek where the 

 formation was first observed, and passing in succession to the south, east, and 

 north sides of the Hills. 



