formations of the Middle Cretaceous. 321 



" Belly River," will best be adhered to in all discussions regard- 

 ing the geology of this region. In respect to the upper por- 

 tion of the middle Cretaceous, the tendency of the Canadian 

 Survey has, for some time, been in accord with the suggestions 

 urged for acceptance in the preceding pages, — that is, toward 

 the grouping together of the Fort Pierre and Fox Hills forma- 

 tions, but under the designation " Pierre (including Fox Hills)" 

 rather than under a new term, employing the name, Fox Hills, 

 to denote only the upper sandstones of the series, lithologically 

 considered : this system of nomenclature is obviously open to 

 the same criticism as that employed by Dr. White, namely, a 

 confusion of ideas, necessarily resulting from the use of terms 

 already long applied in an entirely different manner. 



To briefly compare, now, with the foregoing the merits of 

 the group names suggested in the present paper. 



1st, That of " Colorado " : this is retained on account of its 

 long established usage and the impossibility of finding a term 

 more suitable to the demands made upon it by the principles 

 upon which it is to be employed ; it has, indeed, had a signifi- 

 cation different from that now assigned it, but this is by no 

 means universally accepted, and hence cannot be considered an 

 obstacle to its employment when really found desirable from 

 every other point of view. 



2d, The term, " Montana " : In the first place, as a name, it 

 is of equal rank with those of the other general divisions of 

 the Cretaceous as proposed in the present paper, that is, with 

 the Dakota, the Colorado, and the Laramie, though of rather 

 greater geographical value than the last ; in the second place, 

 it is an especially appropriate term from the facts, (a) that in 

 the territory of Montana a large part of the surface area is 

 occupied by one or the other of its sub- divisions, between 

 which, here, as elsewhere, it is impossible to draw a definite 

 line of separation, either lithologically or paleontologically, 

 and (b) that Montana contains a relatively greater proportion 

 of. the outcrops of this formation than any other region of the 

 Northwest, with the possible exception of the British North- 

 west Territory ; finally, there is the argument from its early 

 discovery and study in this very area, an argument upon the 

 principles of which, geological nomenclature has often, from 

 the earliest times, been based. 



In the foregoing facts, therefore, there exist the strongest 

 grounds for the adoption within the United States of the 

 method of grouping the middle Cretaceous formations advo- 

 cated in this paper, and for the admission into geological 

 literature of North America, of the name — Montana— as a 

 designation of one of the more comprehensive divisions of the 

 Cretaceous system. 



Am. Jour. Sci.— Third Series, Vol. XXXVIII, No. 226. — October, 1889 

 21 



