1856.] Ill 



AssiMiNEA. CARiXATA. Testa rcgulariter conica, lutea, vittata, subcrassa ura- 

 bilicata, laevi ; spira ad apicera acuta ; suturis paulisper impressis, infra lineatis ; 

 anfractibus instar septenis, planulatis ; apertura elliptica, subcanuliculata, iutus 

 vittata ; umbilico spiraliter carinato ; columella incurvataad basim subangulata. 



Hah. Siam, S. R. House, M.D. 



' Desa-iptions of New Species of Acephala and Gasteropcda., from the Tertiary forma- 

 tions of Nebraska Territory, loith some general remarks on the Geology of the 

 country about the sources of the 3fissouri River. 



By F. B. Meek and F. V. Hayden, M. D. 



That portion of the great Tertiary basin from which the fossils described in 

 the following- paper were obtained, occupies an extensive area of country near 

 the head waters of the Missouri, chiefly between the 46th and 49th parallels of 

 north latitude, and the 100th, and 108th degree of longitude west from Green- 

 wich. According to the Barometrical measurements made by the party charged 

 with the exploration of the proposed northern route of the Pacific railroad, this 

 district varies in its elevation from 1800 to 2700 feet above the present flow of 

 the tidal wave.* 



In regard to the geographical, topographical, and phj'sical features of this 

 country, its native tribes, its botany, zoology, &c., much interesting information 

 was long since laid before the public by the reports of Lewis and Clark's and 

 Long's expeditions, by Mr. Catlin, the Prince of New Wied, Mr. Nuttall and 

 others. More recently, much information of a similar nature has been added by 

 the report of the Pacific Railroad Survey. All these enterprising travellers 

 mention the occurrence of sandstones, clays, lignite, &c., but without giving us 

 much information in regard to the age of these formations, the extent of country 

 occupied by them, or as to the character of their organic remains. 



In 1849 Dr. John Evans traced a great Lignite formation from below Fort Clark, 

 along the Missouri to a point twenty miles below the mouth of the Yellow Stone; 

 and in 1850 Mr. Thaddcus A. Culbertson, who visited this country under the 

 patronage of the Smithsonian Institution, saw this formation at two or three 

 points above Fort Union. In a map accompanying a highly interesting memoir 

 on the geology of the Hudson's Bay Territories, published recently by Mr. A. K. 

 Isbister, in the Journal of the Geological Society of London, a large area about 

 the sources of the Missouri, is colored as Tertiary, but so as to convey an in- 

 correct idea of the extent of country occupied by it. About the same time, Mr. 

 Jules .Marcou published in the Bulletin of the Geological Society of France, a 

 memoir on the Geology of the United States and the British Provinces, accom- 

 l^anied by a map, on which he colors nearly all the country about the headwaters 

 of the Missouri as New Red Sandstone, surmounted along the west shore of that 

 stream by Cretaceous outliers. Between this and the Black Hills he brings up 

 to Cannon-ball River, from the White River basin, a continuous belt of Tertiary. 

 West of this he places a belt of Jurassic, and along the supposed position of 

 the Black Hills he runs a stripe of Eruptive and Metamorphic rocks, flanked on 

 the east and west by Carboniferous formations. On the west side of the Black 

 Hills he colors another extensive district of Jurassic. In all this Mr. Marcou 

 is certainly mistaken, excepting in regard to the Eruptive and Metamorphic rocks 

 of the Black Hills ; there may also be Carboniferous formations tliere, but 

 they have not yet been recognized as far north by two or three hundred miles, 

 as laid down by him. 



Leaving for a future occasion all local and other details, we now propose to 

 give a brief general sketch of the extent and boundaries, as far as we can, of 

 that porticn of the great Tertiary lignite formation from which our fossils were 

 collected, with a few remarks wpon its probable age, and relations to the White 

 river basin, as well as to the Cretaceous formations upon which it reposes. 



* Some points not crossed by these explorers may be a few hundred feet higher. 



