392 N. H. DARTON — JURASSIC FORMATIONS OF THE BLACK HILLS 



Southern margin of vplift. — Along the southern margin of the uplift 

 there are extensive exposures of the Jurassic beds which present inter- 

 esting features. The following section made near Minnehahta Station 

 is typical for a wide area : 



Beulah shales. 



Grayish fi;reen shales with thin fossiliferons Hmestone 



layers 105 feet thick. 



Red sandstone with some red and green shales 75 



Pale greenish buff sandstones, thin bedded 10 



Pale grayish green shales 10 



Buff, flaggy sandstones, ripple-marked 35 



Gray shales 40 



Red sandstone, coarse, massive, fossiliferous 25 



Red beds. 



The basal red sandstone is a conspicuous member for several miles 

 west, but towards Pass creek it finally thins out and disappears. Its 

 aspect near Red canyon is shown in plate 42, which shows also the con- 

 tact with the Red. beds. 



Vicinity of Newcastle and Cambria. — Along the western slope of the 

 Black Hills near Cambria the formation presents the following average 

 section : 



Beulah shales. 



Green shales with fossiliferous calcareous layers 120 feet thick. 



Red sandy shales 50 



Thin sandstone and shales 25 



Light buff, slabby sandstone, ripple-marked 25 



4 Greenis hgray shales 60 



\ Red beds. 



These features continue far to the north, with some variation in thick- 

 ness and minor changes in local included beds. The deposit as a whole 

 becomes somewhat more arenaceous and thickens. 



Section in Belle Fourche valley. — The following section in the Belle 

 Fourche valley is by Newton. It includes at the top a considerable 

 thickness of the Beulah shales. 



Clay or marls, yellowish green and gray, sometimes 

 sandy, Avith streaks of purple near top . . 140 feet thick. 



Sandstone, brown, lamellar 3 " " 



Clay or marl, brownish and sandy 15 " " 



Limestone, thin stratum, very fossiliferous 



Clay or marl, yellow with red sandy clay at base, 

 exposure not complete 235 " " 



