BLACK HILLS GEOLOGY. 



199 



STRATIGRAPHIC SECTION. 



Section at Elmore. 



fl. 



I 



2 1 



Directly underlying the Carbon- 

 iferous is a pinkish, very evenly 

 bedded limestone. It is quite 

 massive, contains no fossils and 

 is extremely soft. Seams of a 

 white, hard, cherty material run 

 through it parallel to the lamina- 

 tion, and are often quite persist- 

 ent. They sometimes attain a 

 thickness of 6 inches. 



2. Compact purplish to white and 

 lilac-colored limestone, quite 

 pure and highly fossiliferous. 

 Contains crinoids and Produchis. 



A 

 I 



Talus of large limestone blocks 

 which have fallen from above. 



V 



Alternating shales and shaly sand- 

 stones of varying thickness often 

 glauconitic and prevailingly red- 

 dish or yellowish from oxide of 

 iron. Limestone conglomerates 

 or breccias termed interforma- 

 tional conglomerates also occur, 

 but are not confined to any one 

 horizon and are not persistant 

 features. 



Feet. 

 40 



20-j- 



75 + 

 20 -|- 



15 



250 



18+ 



Section from Crown Hill. Port- 

 land, AND Mine Shafts. 



Crown Hill. 



Sandy limestone of a yellowish color 

 containing JMaclurea magna, and 

 many large Orthoceratites, Haly- 

 sites catenularis and other un- 

 identified fossils. Thickness un- 

 determined. 



Fine slate-colored limey shales 

 breaking into exceedingly minute 

 fragments of great thinness. 



Scolithus sandstonee heavy-bedded 

 and of indefinite thickness. 

 Forms top of the unquestioned 

 Cambrian. Contains borings of 

 ScolitJms linearis, but these may 

 be absent. Locally known as 

 the " worm-eaten " or " upper" 

 quartzite or as the " upper con- 

 tact." 



Reddish shales and shaly sand- 

 stones. 



Mine Sections at Rua, Union, Big 

 Bonanza, etc. 



Reddish, sandy, crystalline lime- 

 stone locally known as "sand- 

 rock." It is exceedingly calcar- 

 eous, and when unoxidized forms 

 hard, compact, bluish material 

 which is termed blue " sand- 

 rock," but is in reality a crystal- 

 line limestone. 

 Hard quartzitic conglomerate coarser 

 at the base and lying unconform- 

 ably on the Algonkian series. 



464 



