white.] INTRODUCTORY REMARKS. 9 



period in the geological history of North America, were studied independ- 

 ently by different investigators, at various more or less widely-separated 

 localities within the region that has just been indicated, which resulted 

 in the strata of that group receiving different names in different regions. 

 Thus, Meek & Hayden gave the name "Judith River Group" to those 

 strata in the valley of the Upper Missouri, near the mouth of Judith 

 River, which were found tocoutain brackish-water fossils. They gave 

 the name "Fort Union Group" to strata of similar faunal character 

 near Fort Union, also in the valley of the Upper Missouri, but at a con- 

 siderable distance to the eastward of the Judith River region. They 

 also gave the name "Lignitic Group" to those strata in Colorado east 

 of the Rocky Mountains which were found to contain a similar fauna. 

 Professor Powell, studying the strata in Wyoming and Utah, gave the 

 name" Point of Rocks Group" to a series which agrees mainly with that 

 which' is now called Laramie, and which had been referred to by Meek 

 & Hayden as the "Bitter Creek Coal series." The strata which are 

 herein called the Bear River Laramie beds of Southwestern Wyoming 

 and the adjacent parts of Utah were by Meek and Hayden generally re- 

 ferred to as the "Bear River Estuary beds." Mr. King was the first to 

 place all these local groups together (except those of the Upper Missouri 

 River region) under the general and comprehensive name of Laramie 

 Group. I subsequently showed that the Judith River, Fort Union, Lig- 

 nitic, and Point of Rocks groups are all connected together by specfiic 

 identity of fossils in their respective strata.* I have therefore treated 

 the strata of all those different regions respectively as only local devel- 

 opment of parts of one great group; but I have retained the local names 

 which they originally received from different authors, only substituting 

 the word "beds" in most .of those cases for that of "group," using the 

 latter term in the more comprehensive sense. Thus, I speak of the Judith 

 River beds, Fort Union beds, Bear River beds, &c, while referring them 

 all to the great Laramie Group. 



A similar duplication of names, arising from similar circumstances, 

 also exists in reference to the earlier or earlist members of the purely 

 fresh-water Eocene series, which immediately succeeds the Laramie 

 Group. Thus, the names " Wahsatch Group" of Hayden, "Vermilion 

 Creek Group " of King, and " Bitter Creek Group " of Powell are re- 

 garded as substantially equivalent, or as representing one and the same 

 division of the Eocene epoch. 



To aid the reader, who may be assumed to be unfamiliar with the 

 details of western geology and with the names which the different 

 series of strata in the West that are necessarily often referred to in 

 this article have received from different investigators, the following 

 summary of facts and opinion is given: 



1. The "Judith River Group," " Fort Union Group," " Lignitic Group," 



*An. Rep. U. S. Geol. Sur. Terr, for 1877, pp. 25.2-265. 



