WHITE.! LARAMIE GROUP. 33 



from the greater, lower portion of the series, and placed with the Wasatch 

 Group above it. This was done because of an uncouformity of the two 

 portions in that district, and an entire conformity of tliat upper portion 

 with the strata of the Wasatch Group above it, although the affinities 

 of the fossils of that ui)per portion are with those that are found be- 

 neath, rather than with those of the Wasatch Group above. After a 

 careful examination of the extensive exposures of this series of strata, 

 as well as those oif the Wasatch Group above it in this district, I have 

 failed to discover any unconformity, such as exists in the valley of Bit- 

 ter Creek. Therefore, the greatest unconformity that is now known to 

 exist among any of the strata from the base of the Cretaceous to the 

 top of what I here designate as the Post-Cretaceous, is found among the 

 strata of the latter group, and not at its top. In this district and the 

 region immediately adjoining it, whatever catastrophal or secular changes 

 may have meanwhile taken place elsewhere, or even extending within 

 its limits, sedimentation was evidently continuous and unbroken, not 

 only through this series itself, but also into and through the whole 

 Wasatch Group also. 



The fact that this series passes insensibly into the Fox Hills Group 

 below, and into the Wasatch Group above, renders it difficult to fix upon 

 a strati graphical plane of demarcation, either for its base or summit. I 

 have therefore decided to regard this group as essentially a brackish - 

 water one, referring all strata below, that contain any marine Cretaceous 

 invertebrate forms, to the Fox Hills Group, beginning this series with 

 those strata that contain brackish- and fresh-water forms, and ending it 

 above with those strata in which the brackish-water forms finally cease. 

 Thus defined, the whole series seems to form one natural paleontologi- 

 cal group, as well as to be a sufficiently distinct stratigraphical one, for 

 which I have adopted the name of Laramie Group of King. 



My reasons for separating this group from the Cretaceous series, 

 where it has been placed by Cope, King, and Powell, and for giving it 

 the provisional designation of Post-Cretaceous, have been discussed by 

 me in Article XXIV, Vol. Ill, No. 3, Bulletin of the United States Geo- 

 logical and Geographical Survey of the Territoiies, but they may be 

 briefly repeated here. The flora of this group is untlerstood to be wholly 

 of Tertiary types, according to Professor Lesquereux. None of its in- 

 vertebrate fossils are of distinctive Cretaceous types, although fossils of 

 similar types are known to occur in Cretaceous as well as Tertiary strata. 

 So far, then, as the flora and invertebrate fauna are concerned, there is 

 nothing to indicate the Cretaceous age of the group. In fact, Inverte- 

 brate Paleontology is utterly silent upon the subject. On the contrary 

 Professor Cope finds reptilian remains, even in the uppermost strata of 

 the group, that he regards as of Cretaceous type. 1 believe that, upon 

 the evidence of invertebrate paleontology, the Fox Hills Group is later 

 than the latest Cretaceous strata of Europe ; and I therefore regard the 

 Laramie Group as occupying transitional ground between the well- 

 marked Cretaceous and Tertiary groups, but this opinion is only tenta- 

 tively held until further facts are obtained. 



THE LARAMIE GROUP. 



The relations of the Laramie Group to those immediately above and 

 below it in the geological series, as well as its general characteristics, 

 have been pointed out in the last paragraphs, and it now remains to 

 speak of its characteristics as they are shown in this district and those 

 adjoining it. 



The Laramie Group, in a large part of Southern Wyoming and the 

 3 G 



