240 REPORT UNITED STATES GEOLOGICAL SURVEY. 



out modifying their types, and affected all or nearly all tlie marine 

 species also. 



A marked contrast between the invertebrate fauna of the Coalville 

 series and that of the whole Upper Missouri River series is shown in the 

 almost entire absence of Cephalopods from the former, while the profus- 

 ion and great variety of such forms constitutes a marked faunal feature 

 of the latter. It is hardly to be expected that the equivalents of those 

 Coalville strata, even in that immediate region, will be found to be quite 

 so deficient as the present collections indicate, but a comparative pau- 

 city of them there is doubtless the rule. There is also a considerable 

 contrast between the Cretaceous invertebrate fauna of Texas, and the 

 territories adjacent, and that of the Upper Missouri Eiver region, but 

 with which that of the Coalville region has no greater affinity than with 

 the former. 



The contrast between the invertebrate Cretaceous fauna of the Coal- 

 ville region and that of the Upper Missouri Eiver region, together with 

 its representatives in Colorado and Wyoming, has a parallel in the dif- 

 ference between the invertebrate fauna of the Laramie Group as repre- 

 sented in the valley of Bear Eiver and that of the same group in those 

 other regions which have been already discussed in this report ; and the 

 contrast in both cases is probably due to similar causes. 



From the valley of the Weber I proceeded northward to that of Bear 

 Eiver, for the purpose of examining the Laramie strata there. The 

 strata of this group have been much displaced in the region bordering 

 the western side of Green Eiver Basin, and the areas of surface upon 

 which they are exposed are few and small compared with those more 

 eastern regions of the Laramie Group which have already been noticed. 

 This displacement of the Laramie strata has caused them to be uncon- 

 formable with the Wasatch beds that rest upon them, the degree of 

 unconformity being great in some places and only slight in others. This 

 condition of the strata will be considered on a subsequent page, in con- 

 nection with the apparently uninterrupted deposition of both the Lara- 

 mie and Wasatch Groups farther eastward. The only localities of 

 Laramie strata which I visited in this region are in two neighborhoods 

 a few miles apart, in the valley of Bear Eiver. The principal of these 

 localities are in the neighborhood of the crossing of the Union Pacific 

 Eailroad, near Mellis Station on that railroad, and also near the mouth 

 of Sulphur Creek and some eight or ten miles southeastward from Evan- 

 ston, Wyo. The Laramie strata exposed in this neighborhood are those 

 which are represented by Mr. Meek in No. 28 of his section of the rocks 

 of that vicinity, as shown on page 451, An. Rep. U. S. Geol. Sur. Terr. 

 for 1872, and which have become so generally known as the " Bear Eiver 

 Estuary Beds." They are there about 500 feet in thickness, and con- 

 formably with them, in upward order, about 200 feet in thickness of dark : 

 gray shales occur, which contain t#liost fish-scales ; but no other fossils 

 were obtained from them. My examination of this neighborhood added 

 little to a knowledge of these strata beyond that which had already been 

 published by Mr. Meek and Mr. King, except that 1 found them quite 

 fully exposed on the west side of the river, which fact is not shown on 

 Mr. King's map, nor mentioned by Mr. Meek. My collections, however, 

 embrace some species not before known. 



The Laramie strata of the other neighborhood comprise the exact 

 equivalents of those near Mellis Station, and contain an abundance of 

 the same fossils, together with the Evanston coal series, the best develop- 

 ment of which appears at the little hamlet of Almy, three miles north- 

 ward from Evanston. From that point to about four miles farther north- 



