388 N. II. DARTON JURASSIC FORMATIONS OF THE BLACK HILLS 



Fossils also occur in the sandstone. The remains are molluscan, with 

 the exception of Pentncrinoides aristlcus, and bone fragments. 



FOSSILS OF THE FORMA TION 



The following is the list of the fossils so far reported : 



Ammonites cordiformis Pleuromya newtoni 



Ammonites Jienryi Protocardium shumardi 



A starfe fragilis Psammobia prematura 



Asiarte inornata Pseudomonotis curta 



Asterias dubium Pseudomonotis orbiculata 



Avicida mucronata Rhynchonella gnathophora 



Belemnites densiis Rhynclionella myrina 



Camptonecies bellistriatus Saxicava jurassica 



Cainpionectes extenuatus Tancredia xquilaleralib 



Dosinia jurassica Tancredia bulbosa 



Gei'viUia recta Tancredia corbidiformis 



Grammatodon inornatus Tancredia inornata 



Lingula brevirostris Tancredia j^ostica 



Lioplacodus veturnu^ Tancredia warrenana 



Myacites nebrascensis . Thracia arcuata 



Mytilus whitei Thracia sublevis 



Nesera longirostris Trapezium bellefourchensis 



Ostrea engelmanni Trapezium subequalis 



Ostrea strigilecula Trigonia conradi 



Pecten neiuberryi Vnio nucalis 



Pentacrinus asteriscus Valvata scarbrida 



Pholodomya humilis Viviparus gilli 



Planorbis veturnus Volsella pertenuis 



GEOLOGICAL SUCCESSION AT VARIOUS LOCALITIES 



Vicinity of Catholicon Springs hotel, Hot Springs. — The stratigraphic varia- 

 tions of the formation were traced with care, but the vertical distribution 

 of the fossils has not as yet been determined. Certain members of the 

 formation are of general occurrence, andthere are others which are less 

 persistent. The succession of the lower dark shales, a slabb}'-, buff, ripple- 

 marked sandstone next above, a reddish, sandy shale, and an upper 

 green shale with fossiliferous limestone layers, is continuous over a 

 wide area. At the base of the formation there is often a massive sand- 

 stone of red or buff color occurring in extended lenses and often attain- 

 ing a thickness of 25 feet. Next above are the shales just mentioned, 

 and it is in the sand}^ la3^ers at the base of these sliales, near Hot 

 Springs, that I discovered the fossil fish described by Doctor Eastman 

 in his pa,per which follows mine. The locality is about one mile east- 

 southeast from the Union railroad station, or one-half mile south of the 



