42 



a three-foot bed of coal. In the specimens of this shale, I was some- 

 what surprised to find two of the same Oyrenoid shells that occur in an 

 exactly similar shale over one of the coal-beds at Hallville, on the Union 

 Pacific Railroad, in Wyoming', five hundred miles farther westward, 

 and at about 2,800 feet. greater elevation above tide. The specimens of 

 shale from these two localities are exactly alike in all respects, and the 

 fossils contained in them are not only beyond question the same species, 

 but so precisely similar in their state of preservation that it would be 

 quite impossible to distinguish in any way the collections from the two 

 localities. 



The specimens from the other horizon, 45 feet below the surface, in 

 this shaft, consist of a conglomeration of shells, with merely enough 

 gray clay, and some sand, to fill the interstices. The shells, so far as 

 seen, are all bivalves, generally in so tender a condition that it is very 

 difBcult to separate any of them from the matrix in a good state of pre- 

 servation, though they were evidently, in most cases at least, not broken 

 or water-worn before being buried in the mud and sand forming the 

 stratum in which they are found. They consist, so far as determined, 

 of an Anomia, and perhaps two or three species of Cyrenoid shells, with 

 a few fragments of other undetermined bivalves. The Anomia I believe 

 to be identical with a species found at Black Butte station, Wyoming, 

 on the Union Pacillc Railroad, only about two miles east of Hallville 

 coal-mines, and perhaps 600 to 800 feet higher in the same series. The 

 Cyrenoid shells are also closely allied to, and possibly in some cases 

 identical with, forms found at Black Butte station. 



A single fragment of a bivalve, found among the specimens, consist- 

 ing of most of the hinge of a right valve, certainly belongs either to the 

 genus Cyprina or VenieUa (= Venilia, Morton). The hinges of these two 

 types are so similar in some of the species that it is not always easy to 

 distinguish the two without pretty good specimens, or at least such as 

 give a moderately clear idea of the form and ge;ieral external appear- 

 ances of the shell. The specimen mentioned does not show the posterior 

 lateral tooth ; but its cardinal and anterior lateral teeth are very similar to 

 those of Yeniella. The scar of its pedal muscle, however, seems to be 

 very nearly, if not quite, connected with that of the anterior adductor, 

 as in Cyprina. I regret very much that I conld not find an entire valve 

 of this shell among the specimens, so as to be able to decide the ques- 

 tion in regard to which of these two genera this shell really belongs ; 

 because, if it is a Yeniella, it would furnish a strong argument in favor 

 of the conclusion that this whole formation belongs to the Cretaceous 

 period, and not to the Tertiary ; if a Cyprina, however, it would prove 

 nothing either way, that genus being common to both Cretaceous and 

 Tertiary rocks, as well as to our existiug seas. 



That the formation from which these fossils came, however, is the same 

 as the Bitter Creek series of Wyoming, including the Black Butte beds, 

 the Hallville coal-mines. Point of Rocks, and Rock Spring coal-mines, 

 &c., I have scarcely a shadow of doubt; and the determination of this 

 fact is one of considerable interest in several points of view. In the 

 first place, it shows that the Bitter Creek series, that contains such val- 

 uable deposits of an excellent quality of brown coal, extends far out 

 under the plains east of the Rocky Mountains, and at least holds out a 

 reasonable prospect that valuable deposits of this useful substance may 

 be found by sinking shafts in these treeless plains (if the discovery has 

 not already been made*), where a good supply of fuel is of such great 



* I do not know whether workable beds of coal were found iu the shaft already 

 sunk or not. 



