GEOLOGICAL SURVEY OF THE TERRITORIES. 435 



Devil's Slide, Montana, iire evidently all of Jnrassic age. They are 

 nearly all bivalves, and belong to genera that also occur in the (Jreta- 

 ceons, and in part in older formations than the Jurassic, as well as in 

 more modern rocks than the Cretaceous. None of them are, beyond 

 doubt, identical with foreign Jurassic species ; but from their specific 

 afifinities to European Jurassic forms, and their positive ideutitj', in a 

 few instances, with species found at other localities in the West, in well- 

 determined Jurassic beds, as well as from the entire absence among 

 them of any strictly Cretaceous types, we can safely refer the rocks iu 

 which they occur to the Jurassic. 



Sjiring CaTion. — The few specimens from the upper beds at Spring 

 Canon are probably also Jurassic types, but the number and condition 

 of the specimens scarcely warrant the expression of a i)Ositive opinion 

 on this point. 



Those from the lower beds near Fort Hall, Idaho, although all belong- 

 ing to one species, evidently came from a Jurassic rock ; while a few 

 casts from the upper beds at thfe same locality, also, seem to belong to 

 the same epoch ; but the specimens being all casts, cannot be satisfac- 

 torily studied. 



CRETACEOUS AGE. 



Coalville. — The coal-bearing rocks at Coalville, Utah, are undoubtedly 

 of Cretaceous age, as stated by Mr. King and Mr. Emmons, and as was 

 from the first maintained by myself. During the past summer I had 

 an opportunity to examine, personally, this interesting locality, and to 

 note the thickness, order of succession, and composition of the great 

 group of beds exposed there, as well as to collect and study a large 

 series of the organic remains found in the same. From these observa- 

 tions it is now proposed to give, below, some remarks on this extensive 

 series, in more detail than has hitherto been done. Before proceeding 

 to do so, however, it seems desirable that a few words should be said in 

 regard to what has been already published respecting the geological age 

 , of this formation, as there would at least appear to be some misappre- 

 hensions on this point. Perhaps the shortest waj^ to place this prelimi- 

 nary^ information before the reader will be to quote from Dr. Hayden's 

 Eeport of 1870, page 299, the following paragraphs, written by myself, 

 on this coal series, in a paper contributed to that report : 



Some of the specimens from near Bear River, aud at Coalville, Utah, from a light 

 colored sandstone, containing beds of a good quality of brown coal, appear to lielong 

 to a member of the Cretaceous series not corresponding to any of those jjamed in the 

 Upper Missouri country, though it is, as I believe, represepted by a similar sandstone 

 under the oldest Estuary Tertiary beds at the mouth of Judith River, on the Upper 

 Missouri. In 18C0, Colonel Simpson brought from this rock, on Sulphur Creek, a small 

 tributary of Bear River, in Utah,* several casts of Inoceramtis and other fossils; and 

 in some remarks on Colonel Simpson's collection, published by the writer, in connection 

 with Mr. Henry Engelmann, the geologist of Culonel Simpson's survey, we referred 

 this formation to the Cretaceous. t The collections that have been brought in from 

 Utah, by Mr. King's and Dr. Hayden's surveys, contirm the conclusion that it belongs 

 to the Cretaceous, as they contain, amongother things, species of Inoccramns, Anchura, 

 and Gyrodes — genera that seem not to have survived the close of the Cretaceous period. 

 In addition to this, there is among Dr. Hayden's collections from this rock, at Coal- 

 ville, a TurriteUa that I cannot distinguish by the figure and description, even specifi- 

 cally from T. Martinezensxs, described by Mr. Gabb, from one of the upper beds in Cali- 



* This locality on Bear River is really within the western border of Wyoming, 

 though it was supposed by me at the time of writing this paragraph to be, like Coal- 

 ville, iu Utah. 



t See Proceed. Acad. Nat. Sci., Philad., 1860. 



