(358 REPORT <>F NATIONAL MUSEUM, 1 ( .H>4. 



scribed both above unci below, the main point in dispute being whether 

 it should be relegated to the Cretaceous or the Tertiary. As time went 

 on, but particularly after the organization of the present survey, more 

 careful and detailed work became possible. The Bear River beds were 

 shown by Drs. C. A. White and T. W. Stanton, in 1891, to belong- to 

 the marine Cretaceous; the upper portion in Colorado and Wyoming- 

 was found by Cross, Hills, and Weed to be out of harmony with that 

 beneath, and was relegated to the Eocene-Tertiary; the Laramie proper 

 becoming- more and more restricted as the work of differentiation 

 went on. 



In 1897 Drs. F. H. Knowlton and T. W. Stanton, the one a paleo- 

 botanist and the other a paleontologist, together made a personal 

 inspection of many of the important localities, and, after passing the 

 evidence in review, concluded that the so-called Ceratops beds of 

 Converse County, Wyoming, should be referred to the Laramie group; 

 that the coal-bearing series of the Laramie Plains is older than the 

 "true" Laramie, and, instead of conformably overlying the Fox Hills 

 group, is itself overlain by it. 



The Bitter Creek and Black Buttes beds they considered as belong- 

 ing to the "true 17 Laramie, and also those of Crow Creek, Colorado. 

 while those of Point of Rocks, in the Bitter Creek Valley, were regarded 

 as Cretaceous (Montana). The base of the Laramie (after a review of 

 the opinions of Hatcher, Hills, King, and Hayden) they would place 

 "immediately above the highest marine Cretaceous beds of the Rocky 

 Mountain region,' 1 the top being marked by the Fort Union beds. In 

 other words, the Fort Union beds are now regarded as Eocene and the 

 lower-lying as Laramie Cretaceous. 



Both these workers, it is well to note, conformed to the generally 

 received opinion that "marine invertebrates (fossils) are more accu- 

 rate and definite horizon markers than either plants or nonmarine 

 invertebrates, because they have a less extended vertical and a broader 

 geographic distribution." 



(). C. Marsh, the reader will perhaps remember, had in L891 

 announced the general principle that all forms of animal life are of 

 value as horizon markers "mainly according to the perfection of their 

 organization or zoological rank." Following out this principle, he 

 regarded plants as unsatisfactory witnesses, invertebrates as much 

 better, and vertebrates as the best of all, as offering "reliable evidence 

 of climatic and other geological chansres." 



