254 REPORT UNITED STATES GEOLOGICAL SURVEY. 



The column representing the Upper Missouri River region is added 

 for purposes of comparison, in recognition of the classification which has 

 been established by Harden and Meek for the Cretaceous strata there, 

 as a standard for all the Cretaceous strata of the Western Territories. 

 The existence of the species there which are named in the list is given 

 on the authority of those authors, as I have never yet visited that region 

 in person. The column assigned to Eastern Colorado includes, for the 

 present purpose, only that portion of it, east of the Rocky Mountains, 

 which I visited during the season ; and the same may be said of the 

 column assigned to Northwestern Colorado. The column assigned to 

 Coalville is intended to include the whole valley of Weber River in that 

 neighborhood ; and the one assigned to Bear River Valley includes also 

 the adjacent portion of the Valley of Sulphur Creek up to Milliard 

 Station. 



In the table of the Laramie fossils next following, one of the vertical 

 lines separating the columns which represent localities or regions is 

 made double, to indicate the fact that those upon one side of it are east, 

 and those upon the other side of it west, of the Rocky Mountains. Such 

 a modification might be made in this one, but it is hardly necessary, 

 because few facts are more patent than that the elevation of the Rocky 

 Mountains began long after the deposition of the latest strata repre- 

 sented in the table. 



It will, of course, be understood that this table embraces only the col- 

 lections made either by myself or others at the localities which I visited 

 during the season of 1877. It not only does not represent the full geo- 

 graphical distribution of those species, but it is probable that many 

 other species will yet be found in some of the localities which have been 

 thus visited. There is a notable paucity of the species of the Colorado 

 Group represented in the table. This is in large part due to the fact 

 that its strata in the region I traversed are less fossiliferous than those 

 of the Fox Hills Group are ; partly to the fact that, being softer, they 

 are less freely exposed, and partly, that they came less in the way of my 

 season's investigations. 



The construction of the following table of the Laramie fossils which 

 have been collected from the various regions visited by myself during 

 the season of 1877 is similar to that of the preceding table of the Cre- 

 taceous fossils. The species are not only thus tabulated for a synopti- 

 cal view, but the table shows the present known extent of their geo- 

 graphical distribution, and demonstrates the fact that all the principal 

 brackish-water beds yet known in the Western Territories are members 

 of one comprehensive group of strata representing a great period in the 

 geological history of North America. The two columns representing the 

 Judith River and Fort Union beds, respectively, are introduced for pur- 

 poses of comparison, and to show their geological equivalency with the 

 strata of the other localities. The species indicated in those two col- 

 umns are given on the published authority of Hayden and Meek, as I 

 have not yet visited the Upper Missouri River region in person. The two 

 columns designated respectively as Eastern and Northwestern Colorado 

 are of course intended to include only the species that have been col- 

 lected at the localities which I have visited in person, and which have 

 been discussed on preceding pages of this report. The column assigned 

 to Bitter Creek includes the whole series of Laramie strata there : the 

 differences in the fauna at different horizons of the series having already 

 been shown are not repeated here. The column assigned to Bear River 

 Valley includes the species of both brackish and fresh water beds that 

 are found in the district extending from the mouth of Sulphur Creek to 

 seven miles northward from Evanston, Wyo. 



