130 PROCEEDINGS OP THE ACADEMY OP 



closely allied to 0. Marshii,* a Pecten scarcely distinguishable from P. lens of 

 Sowerby, a small Dentalium, and Belemnites densus, Meek and Hayden. From 

 the identity of some of these species with forms collected by Dr. Hayden at the 

 Black Hills, from beds overlying the red gypsum bearing strata of that region, 

 and associated with other well marked Jurassic types, as well as from the 

 affinities of the new species discovered at the locality under consideration on 

 the North Platte, we have no hesitation in referring these deposits to the 

 Jurassic system, in accordance with the views of Dr. Hayden and one of the 

 writers (F. B. M.) expressed in regard to the beds alluded to at the Black Hills. 

 (See Proceed. Acad. Nat. Sci., Philad'a, March, 1858.) 



Cretaceous Rocks. 



Returning south-westward again to Weber river, in order to follow up the 

 succession of the formations, we find that at a point nearly due east of Salt 

 Lake City, on that stream, and but a short distance north of the locality, where 

 it has already been mentioned that Jurassic bed3 with Pentacrinus occur, out- 

 crops of a Whitish Sandstone were seen, containing in an imperfect condition 

 an Oyster, agreeing in all respects, as far as could be determined, with 0. 

 glabra of Meek and Hayden. This rock, with the same oyster, was also seen 

 some eight or nine miles farther down Weber River; also, on White Clay Creek, 

 a tributary of Weber River, and some fifty miles farther east on Sulphur Creek, 

 a tributary of Bear River. At the latter locality a small Anomia was also 

 found with the same Oyster ; and in a more yellowish portion of the same for- 

 mation several specimens of Inoceramus, closely allied to the Western species 

 usually referred to /. problematicus. Judging from the Oyster occurring in 

 this rock, and from its lithological characters, it would seem to be of 

 the same age as some older Cretaceous strata, at the mouth of Judith River, on 

 the Upper Missouri, which have been referred by Dr. Hayden and one of the 

 writers ; provisionally to No. 1, of the Nebraska section. 



At several of the localities rather extensive beds of excellent brown coal, 

 with some shale, were seen in immediate contact with this Oyster Sandstone, 

 and apparently dipping at the same angle, so as to give the impression, when 

 examined, that it belongs to the same epoch. 



Well marked Cretaceous rocks were seen at a point on the Platte below 

 the Red Buttes, near the Platte Bridge. The beds consist of gray shales and 

 slates. The fossils found here are a large new species of Inoceramus, a 

 fragment of a much compressed Baculite and Ostrea congexta of Conrad. From 

 the presence of the latter fossil, it is more than prabable these beds are on a 

 parallel with No. 2 or 3 of the Nebraska Cretaceous series. 



Tertiary Rocks. 



Tertiary formations occur over a large area in the region of Fort Bridger. 

 They seem to belong to two distinct epochs, the older of which was seen on 

 Bear River, near the mouth of Sulphur Creek, about 30 miles west of Fort 

 Bridger, and but a short distance from the locality, already mentioned, where 

 the Oyster and Inoceramus occur in a yellow sandstone. The outcrop seen 

 here consists of light colored and gray argillaceous shale, with coarse dark and 

 light colored limestones, all of which dip at a high angle. The fossils collected 

 from these beds consist of one new species of Unio, three of Corbula (Potarno- 

 i.iya), three species of Melanin, three or four of Paludina, and one of Melampus. 



This is an exceedingly interesting deposit, which is undoubtedly of brackish- 

 water origin, the fossils belonging to just such a group of genera as we would 

 expect to find in an estuary deposit, without any strictly marine forms. One 



*The oyster here alluded to, is distinct from the species referred by Mr. Marcon to 

 O. Marshii. The O. Marsha of Marcon holds a much higher stratigraphic position than 

 . the above mentioned species. 



[April, 



