GEOLOGICAL SUR^^Y OF THE TEREITOEIES. 455 



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termine, none of tlie species from this locality seem to be certainly 

 identical with any of tbose from any of the recognized subdivisions 

 of the Upper Missouri Cretaceous, but some of them occur at other 

 localities along with the characteristic forms of the Benton group. 



Cinnabar Mountain. — The species from Cinnabar Mountain, Yellow- 

 stone Yalley, belong, almost certainly, to the same horizon as those from 

 Missouri Eiver below Gallatin, the species of Trigonia mentioned from 

 that locality being the same found at this. There can be little doubt in 

 regard to these fossils belonging to the Fort Benton group of the Cre- 

 taceous, because 1 recognize among them ScapMtes ventricosus, one of 

 the most characteristic fossils of that horizon. 



Bridge)' Feak. — The few things from eastfootofBridger Peak, (four miles 

 from Fort Ellis.) Montana, are nearly all mere casts in a bad state of pre- 

 servation, but, so far as I have been able to determine, none of the 

 species appear to be identical with any of those known from the recog- 

 nized subdivisions of the Upper Missouri Cretaceous ; though, from their 

 general facies, there is still little room to doubt that they belong to the 

 Cretaceous system. They are certainly not Tertiary. 



Colorado Springs. — A small collection from Colorado Springs, Colorado, 

 evidently belong to the horizon of the Fort Pierre group of the Upper 

 Missouri Cretaceous series. 



Roclc Creek. — The collections found by Professor Lesquereux on Eock 

 Creek are all Cretaceous forms from the horizon of the Niobrara division 

 of the Upper Missouri. 



Fort Marker. — Those collected by him from near Fort Barker are also 

 Cretaceous, and from the horizon of the Fort Benton group. 



Bitter Creek series. — Along Bitter Creek, (a small tributary of Green 

 Eiver, in Wyoming,) from Black Butte northwestward to Salt Wells 

 Station on the Union Pacific Eailroad, and at Eock Spring and some 

 other points west of Salt Wells, there is an extensive series of rocks, in 

 regard to the age of which somewhat difi'erent opinions are entertained. 

 For a detailed description and sections of this formation the reader is 

 referred to Dr. Bannister's report, forming a following section of this 

 volume, my object here being merely to say a few words mainly respect- 

 ing the age of this group. In general terms it may be briefly described 

 as a vast succession of rather soft, light-yellowish, lead-gray, and whit- 

 ish sandstones, with seams and beds of various colored clays, shale, 

 and good coal, the whole attaining an aggregate thickness of more than 

 4,000 feet. 



The invertebrate fossils hitherto found at different horizons in this 

 iseries present a mingling of fresh, brackish, and salt-water types, such 

 as GoniobasiSj Viviparus, Corhicula, Corhula, Ostrea, Anomia, and Modiola. 

 All of these genera are found represented, either directly in the same bed, 

 or very nearly so, near the very top of the series at Black Butte Station, in 

 Division E of Dr. Bannisters section. At Hallville, three miles farther 

 west, and 1,600 to 1,800 feet lower in the series, in Division K of the 

 same section, a Corhicula, and another form like a Corhula, both scarcely, 

 if at all, distinguishable from species found in the higher beds at Black 

 Butte, occur in a black slate over a bed of coal. Near the same hori- 

 zon, at Point of Eocks, seven or eight miles farther down Bitter Creek, 

 great numbers of a fine large oyster also occur, above the fourth (or 

 still higher bed) of a series of beds of coal, seen in the face of a nearly 

 perpendicular precipice, about 300 feet above the bottom of the valley 

 on the north side. Three or four miles west of this, and at a horizon 

 probably 500 feet lower, in Division M, of Dr. Bannister's section, there 

 is a bed 15 to 18 inches in thickness, almost entirely composed of mil- 



