Mesozoic and CcEnozoic Geology and Palaeontology. 83 



large scales and other remains of fishes, and numerous specimens of 

 Ostrea congesta, attached to fragments of Inoceramus. Passing down 

 into light yellowish and whitish limestone, containing great numbers 

 oi Inoceramus prohlematicus, I. pseadomytiloides, I. aviculoides, fish 

 scales, etc. Found in the bluffs along the Missouri, below the Great 

 Bend, to the vicinity of Big Sioux River ; also below there on the tops 

 of the hills. Estimated thickness, 200 feet, 



4. Fort Pierre Group, consisting of dark beds of very fine unctuous 

 clay, containing much carbonaceous matter, with veins and seams of 

 gypsum, masses of sulphuret of iron, and numerous small scales, fishes 

 local, filling depressions in the bed below. Lower fossiliferous zone^ 

 containing Ammoyiites complexus, BacuUtes ovatus, B. compressus, 

 Helicoceras mortoni, H. tortiim, H. umbilicatum, H. cochleatum, 

 Ptychoceras mortoni, Fasus vinculicm, Anlsomyon horealis, Amaur- 

 opsis paludiniformis^ Tnocei^amus suhloivis, I, tenuilineatus^ bones of 

 Mosasaurus missouriensis, etc. Middle zone, nearly barren of fossils. 

 Upper part consisting of dark gray and bluish plastic clays, containing, 

 near the upper part. Nautilus dekayi, Ammonites placenta, BacuUtes 

 ovatus, B. compressus, Scaphites nodosus, Dentalium gracile, Crassa- 

 tella, evansi, Cucullcea nebrascensis, Inoceramus sagensis, I. nebras- 

 censis, I. vanuxemi, bones of Jlosasaurus missouriensis, etc. Found 

 on Sage creek, Cheyenne river. White river above the ^lauvaises 

 Terres, Fort Pierre, and out to Bad Lands, down the Missouri on the 

 high country, to Great Bend and near Bijou Hill on the Missouri. 

 Estimated thickness, 700 feet. 



5. Fox Hills Group, consisting of gi-a\^ ferruginous and yellowish 

 sandstone and arenaceous clays, containing ^eZewm^'^eZZa bulbosa, Nau- 

 tilus dekayi, Ammonites j^lacenta, A. lobatus, Scaphites conradi, 6'. 

 nicolletti, BacuUtes grandis^ Busy con bairdi, Fusus culbertsoni, F. 

 newberryi, Aporrhais americana, Pseudobuccinum nebrascense, Mac- 

 tra warrenana, Cardium subquadratum, and a great number of other 

 molluscous fossils, together with bones of 3Iosasaurus missouriensis, 

 etc. Found at Fox Hills, near Moreau river, near Long Lake, above 

 Fort Pierre, along the base of Big Horn Mountains, and on North and 

 South Platte rivers. Estimated thickness, 500 feet. 



In Nebraska the sandstones of the Dakota Group rest directly upon 

 rocks of the age of the Upper Coal Measures, or of Permian Age. 



They described from the Fort Pierre and Fox Hills Groups, at Deer 

 Creek, near the north branch of the Platte river, Leda bisulcata, now 

 Nueulana bisulcata, Gervillia recta, Crenella elegantula, Cardium 

 pertenue, now Protocardia pertenuis, Tellina nitidida, now 3Iactra 



