formations of the Middle Cretaceous. 319 



of knowledge of this formation and the Fort Benton below, 

 in the Northwest Territory, does not seem to justify the group- 

 ing together, in that region, of two such apparently widely 

 different series of beds, yet, with the exception noted for Man- 

 itoba, it serves well the purposes of the geologists of the 

 United States, in supporting the argument for a division of the 

 middle Cretaceous at the line suggested in the present article, 

 namely, that of the Niobrara and Fort Pierre ; secondly, that 

 portion of Dr. Dawson's remarks which has reference to the 

 relations between the Fort Pierre and Fox Hills formations is 

 thoroughly consistent with the facts as developed within the 

 area of the United States in regard to these two formations, 

 and at once becomes available in support of so much of the 

 argument of this paper, as bears upon the establishing of a 

 comprehensive group to include these formations. 



If, now, a group is constructed out of the upper two forma- 

 tions of the middle Cretaceous (a step which is undoubtedly 

 warranted by the foregoing facts), an important point will be 

 gained in the direction of simple geological classification, — there 

 will be for the entire North American continent a single, com- 

 prehensive term for two most closely related members of the 

 Cretaceous system. With reference to the first of the observa- 

 tions in the last paragraph, admitting the undesirability of such 

 a grouping for the geology of Canada, it is, nevertheless, 

 strongly advocated for that of the United States, in which the 

 circumstances of deposition and life seem to be entirely differ- 

 ent. 



The methods of classification hitherto employed by the more 

 prominent authorities in western geology are partly at variance, 

 and partly in harmony, with the one here suggested. 



That of the Fortieth Parallel Survey, which includes under 

 the one group, Colorado, the Fort Benton, Niobrara, and 

 Fort Pierre formations — the great clay series, in fact, of the 

 middle Cretaceous — and which retains distinct the Fox: Hills, 

 making it of equal rank with the Dakota, Colorado, and Lara- 

 mie, appears to have been adopted by them on penological 

 rather than paleontological grounds, — the available fossil evi- 

 dence at that time being necessarily very imperfect as compared 

 with the present day, — and because they did not always dis- 

 tinguish the individual formations over the area covered by 

 their explorations. 



Powell, on the other hand, who uses only local names, and 

 does not attempt correlation with the Meek and Hayden groups 

 of the Upper Missouri, divides this clayey series into two sub- 

 divisions, the Salt Wells and Sulphur Creek, and probably 

 leaves the upper portion of the Fox Hills in his Point of Rocks 

 group, which should correspond with King's Laramie. 



