GEOLOGICAL SUEVEY OF THE TERRITORIES. 



General section of the cretaceous rocks of the Northwest 



87 



Divisions and subdivisions. 



Localities. 



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Gray, ferruginous, and yellowish sandstone, 

 and arenaceous clays, containing Belemni- 

 tella bulbosa, Nautilus Bekayi, Ammonites 

 placenta, A. lobatus, Seaphites Oonradi, S. 

 Nicolletti, Baeulites grandis, Busy con Bairdi, 

 Fusus Culbertson, F. Neivberryi, Aporrhais 

 Americana, Pseudo-buccinum, Nebraecensis, 

 Mactra Warrenana, Oardium subquadra- 

 turn, and a great number of other molluscous 

 fossils, together with bones of Mosasaurus 

 Missouriensis, &c. 



Dark-gray and bluish plastic clays, containing, 

 near the upper part, Nautilus Bekayi, Am- 

 monites placenta, Baeulites ovatus, B. com- 

 pressus, Seaphites nodosus, Bentalium gra- 

 cile, Crassatzlla Evansi, Oucullcea Nebrascen- 

 sis> Inoceramus Sagensis, I. Nebrascensis, I. 

 Vanuxemi, bones of Mosasaurus Missouri- 

 ensis, <&c. 



Middlo zone nearly barren of fossils 



Lower fossiliferous zone, containing Ammon- 

 ites complexus, Baeulites ovatus, B. compres- 

 sus, Helioceras Mortoni, H. tortum, H. um- 

 bilicatum, PL. cochleatum, Ptyclwceras Mor- 

 toni, Fusus vinculum, Anisomyon borealis, 

 Amauropsis paludiniformis, Inoceramus 

 sublcevus, I. tenui-lineatus, bones of Mosa- 

 saurus Missouriensis, &c. 



Dark bed of very fine unctuous clay, contain- 

 ing much carbonaceous matter, with veins 

 and seams of gypsum, masses of sulphuret 

 iron, and numerous small scales, fishes, 

 local, filling depressions in the bed below. 



Lead-gray calcareous marl, weathering to a yel- 

 lowish or whitish chalky appearance above, 

 containing large scales and other remains of 

 fishes, and numerous species of Ostrea con- 

 gesta attached to fragments of Inoceramus. 

 Passing down into light yellowish and 

 whitish limestone, containing great num- 

 bers of Inoceramus problematicus, I. pseudo- 

 mytiloides, I. aviculoides, and Ostrea con- 

 gesta, fish scales, &c. 



Dark-gray laminated clays, sometimes alter- 

 nating near the upper part with seams and 

 layers of soft gray and light-colored lime- 

 stone, Inoceramus problematicus, I. tenuiros- 

 tratus, I. latus, I. fragilis, Ostrea congesta, 

 Venilia Mortoni, Pholadomya papiyracea, 

 Ammonites Mullani, A. percarinatus, A. 

 vespertinus, Seaphites Warreni, S. larvce- 

 formis, S. ventricosus, S. vermiformis, Nauti- 

 lus elegans, (?) &c. 



Yellowish, reddish, and occasionally white 

 sandstone, with, at places, alternations of 

 various colored clays and beds and seams 

 of impure lignite ; also silicified wood and 

 great numbers of leaves of the higher types 

 of dicotyledonous trees, with casts of Phar- 

 ella (I) Bakotensis, Axinaea Siouxensis, and 

 Cyprina arenarea. 



Fox Hills, near Moreau Riv- 

 er, near Long Lake, above 

 Port Pierre, along base 

 Big Horn Mountains, and 

 on North and South Platte 

 Rivers. 



Sage Creek, Cheyenne Biver, 

 and on White Eiver above 

 the Mauvaises Terres. 



Fort Pierre and out to Bad 

 • Lands, down the Missouri, 



on the high country, to 



Great Bend. 

 Great Bend of the Missouri, 



below Fort Pierre. 



Near Bijou Hill, on the Mis- 

 souri. 



Bluffs along the Missouri, 

 below the Great Bend, to 

 the vicinity of Big Sioux 

 River; also below there 

 on the tops of the hills. 



Extensively developed near 

 Fort Benton, on the Upper 

 Missouri; also along the 

 latter from ten miles above 

 James River to Big Sioux 

 Biver, and along the east- 

 ern, slope of the Rocky 

 Mountains as well as at 

 the Black Hills. 



Hills back of the town of 

 Dakota ; also extensively 

 developed in the surround- 

 ing country, in Dakota 

 County, below the mouth 

 of Big Sioux Biver, thence 

 extending southward into 

 northeastern Kansas and 

 beyond. 



Feet. 

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The names which are given to these groups, both in the cretaceous 

 and tertiary rocks, are always provisional, and are intended as specific 

 points around which to group such facts as may add to our own knowl- 

 edge from year to year ; and when it shall have been found that any of 

 them have served their purpose, and are no longer needed, they will be 

 dropped from the list. Objections may be made to the use of local geo- 

 graphical names, but they have been found by experience to serve our 



