NATURAL SCIENCES OF PHILADELPHIA. 421 



fossils collected from the sandstone here alluded to, near the Judith River, 

 belong to the genus Inoceramus, Tancredia, Mactra, Baculilfs, &c. ; all of which 

 are distinct from the species yet obtained from any of the known horizons 

 elsewhere. 



la our paper of May, 1857, we pointed out that the Dakota Group, (which we 

 then designated as formation No. 1,) is represented in New Jersey and Alabama, 

 by a series of more or less arenaceous clays and sandstones, with lignite and 

 leaves of dicotyledonous trees.* Since that time Dr. Newberry has traced 

 it from near the Arkansas River, in Kansas Territory, by the remains of its 

 characteristic flora, far into New Mexico, where he found it surmounted by a 

 great thickness of well marked Cretaceous rocks. f Dr. Shumard also thinks he 

 can recognize it in Texas at the base of the Cretaceous series of that state. J 



Fort Benton Group. This formation usually consists of dark grey lamina- 

 ted clays, with thin lighter colored arenaceous partings, and layers and beds of 

 sandstone. Towards the upper part, near its connection with the Niobrara 

 Division above, it sometimes includes intercalated layers of grey limestone in 

 all respects similar to the lower portion of the overlying rock; while at some 

 other places its upper portion passes into a dark shale. It seems to attain its 

 greatest thickness in the vicinity of Fort Benton, where the entire hills eight 

 or nine hundred feet in height appear to be composed of it. Until we can have 

 more exact information, however, in regard to the range of the organic remains, 

 through this great thickness of strata, we must have some doubts in regard to 

 whether there may not also be some representation here of the Dakota Group. 



This seems to be the more probable, when we bear in mind that the rock 

 under consideration, becomes, as already stated, blended with the latter for- 

 mation further south at the Black Hills, and along the Rocky Mountains west 

 of them. 



The Fort Benton Group has a wide geographical extension in the country 

 west of the Mississippi, though neither it nor the succeeding rock above, ap- 

 pears to have any well defined representatives as a distinct formation in Ala- 

 bama, New Jersey and other states east of the Mississippi, as was pointed out 

 by us in May, 1857. \ The highest northern locality at which we have any 

 knowledge of its existence is on the north branch of the Saskatchewan, some 

 thirty or forty mihs west of Fort a la Corne, near lat. 54 north, where Prof. 

 Hinde discovered specimens which were referred by one of us, (F. B. M.,) to 

 this horizon. || We had also previously referred to the same position some 

 specimens discovered by Prof. S. I. Dawson at a locality 250 miles west of Fort 

 Garry, on the Assiniboine River.^[ 



It is known to occur in north-eastern Kansas, as well as in Arkansas, and in 

 1857 we poiutcd out that it is probably represented by one of the beds in Mr. 

 Marcou's section of Pyramid Mountain, in the far south-west. Dr. Newberry's 

 investigations, in connection with Lieut. Ives' Expedition, seem to show that it 



*Proc. Acad. Nat. Sci., Philad., Mar., 1857, p. 117; also, see page 426, of this paper. 



f American Journal Sci. Sec. Ser. vol. xxix, p. '.208, March, 18t>U. 



{See an important paper on ihe Geology of Texas, by Dr. B. F. Shumard, in Trans. 

 St. Louis Acad. Sci., Vol. i. p. 582. It is a source of much regret to those interested in 

 the progress of geological science in this country, ihat circumstances have prevented 

 this able geologist from completing the survey of Texas. 



We have sometimes suspected that the bed in New Jersey containing Venilia Conradi, 

 Scaphites hippociejris, and I' holadomya occidental! s, Morton, might belong to this horizon, 

 from the analogy of thesn species to some of our far western Fort Benton Group forms, 

 but we have been assured that they occur in .Mew Jersey, mingled with other species 

 only found in our upper t'reiaceous beds of Nebraska. 



H See Prof. Hind's Report on Saskatchewan and Assiniboine, Expl, Exp. p. 179. Toron- 

 to, 1859. 



fSee Prof. Dawson's Report on Explorations of the country between Lake Superior 

 and the Red River Settlements, p. 18. Toronto, 1859. 



1861.J 



