408 N. H. DARTON STRATIGRAPHY OF THE BLACK HILLS, ETC. 



Iii the Hartville region the Lower Carboniferous rocks are seen lying 

 on the pre-Cambrian crystalline rocks, and many interesting features of 

 overlap are exhibited. The most extensive exposures are in the deep 

 gorge cut by the North Platte river from Guernsey westward, and the 

 Cretaceous rocks are clearly displayed in an anticlinal ridge which rises 

 on the east side of Old Woman creek. 



Generalized Section of the Rocks of the Hartville Uplift 



Age. 



Cretaceous 



Jurassic 



Triassic (?) or 

 Permian. 



Carboniferous. * 



Algonkian. 



Formation. 



Pierre 



Niobrara. . 

 Carlile' 



Greenhorn. 

 Graneros . . 



Dakota.. . 



Fuson 



Minnewaste 

 Lakota 



Morrison . . 



Sundance \ . 

 Spearfish . . , 



Minnekahta (Per- 

 mian). 

 Opeche (Permian) 



Hartville (Penn- 

 sylvanian to 

 Mississippian). 



Guernsey (Mis- 

 sissippian). 



Principal characteristics. 



Dark shales, with limestone concre- 

 tions. 



Impure chalk and limy shales 



Gray shales, with concretions and 



thin sandstone layers. 

 Hard, impure, slabby limestone . . . 

 Dark shales, with local sandstone 



bed near base. 

 Buff, gray, and reddish, massive 



coarse grained sandstone. 

 Gray, buff, and maroon shales and 



sandstone. 



Gray limestone 



Coarse, buff, massive, cross-bedded 



sandstone. 

 Pale green, gray, purple, and black 



clay, with thin limestone. 

 Buff sandstones and gray clays 

 Bright, reddish brown, sandy shales 



and thin bedded sandstone, with 



gypsum. 

 Thin bedded gray limestone 



Bright red, thin bedded sandstone, 

 with red sandy shale. 



Massive gray limestone, in part 

 cherty, some beds very sandy ; 

 also white, gray, buff, and red 

 sandstone, red shale, and gray 

 limestone near base, and basal 

 red quartzite. 



Conglomeratic quartzite, with over- 

 lying sandstone and massive gray 

 limestone. 



Granites and schists. 



Thick- 

 ness. 



Feet. 

 1,200 



250 

 425 



50 



800: 



60 

 60 



5 



100 



100 



200 

 450 



20 



60 



630 



150 



G UERNSE Y FORMA TION 



The Guernsey formation consists mainly of limestone with a thin series 

 of alternating sandstones and limestones in its lower portion, and at the 



