^^^^TE.] FOSSILS FKOM NORTH PARK. 203 



adjacent to the eastern base of the mountains. They occupy a large 

 area in tht; mountain region between the Front and Park Kanges, extend- 

 ing from near the southern ])ortion of Middle I'ark to the southern por- 

 tion of ISTorth Park, and including the hill region between both. It has 

 been searched for fossils by every geological party that has \isited it, 

 but, so far as Middle Park is concerned, without success except as to 

 fossil plants. 



Among the collections of the survey are some fossils obtained by the 

 late Mr. Marvine, from strata that have been referred to the Laramie 

 Grou}), in Xorth Park, accomjjanied hj the following label : " North 

 Park, SW. corner, 8 miles from Muddy divide." "Muddy divide" is 

 doubtless the locality which is designated as " Muddy Pass " on the max)s 

 of the Atlas of Colorado, lately published by the survey. The fossils re- 

 ferred to consist of two, or perhajjs three, species of gasteropods, which 

 are in a partially crushed and imperfect condition of preservation, being 

 in the form of casts in soft sandstone. One is a Vivqjarus, the specimens 

 of which are remarkably like some of those of V. loyomingeims Meek, 

 which I have collected from the Bridger Group, in a similar state of 

 preservation ; but there is nothing in the observable characters of these 

 specimens that would forbid a reference of them to V. ReynoUManus 

 INIeek & Hayden, from the Fort Union Group of the Upper Missouri 

 Eiver region. The correctness of the latter reference, rather than the 

 former, is suggested by the fact of the known identity of the Fort Union 

 beds with the Laramie Group ; and also the further fact that Y. Wyo- 

 minf/ensis has not been recognized in any other strata than those of the 

 Bridger Group, not even those of either the Green Eiver or Wasatch 

 Group. 



Of the other species, one is referred to Campeloma, and is probably 

 identical with (7. mtiltistriata Meek & Hayden, from the Fort Union 

 beds, and also found by myself in the Laramie strata of Crow Creek 

 Valley. 



The other form is somewhat more elongate than the last, and has a slight 

 angularity at the outer side of its body volution. It i)erhaps belongs to the 

 genus Gouiobasis, but neither its generic or specific characteristics coidd 

 be clearly distinguished. These are all the inveii:ebrate fossils that are 

 known to have been collected from any of the strata of this large intra- 

 mountain area that have been referred to the Laramie period. Of them- 

 selves they are not sufficient to determine the age of the strata contain- 

 ing them, or their equivalency or otherwise with those of the Laramie 

 Group. The strata of all the other areas which in this report are re- 

 ferred to the Laramie period are, as I shall show, so referred because of 

 the specific identity of a greater or less number of species of inverte- 

 brate fossils found in the strata of the different areas or regions respect- 

 ively. This ijaleontological evidence is in all cases corroborated by the 

 stratigraphical relations of the Laramie strata with those of the Fox 

 Hills Groui) beneath, and also, in some cases, with other groups above. 

 In the case of the strata of Middle Park of assumed Laramie age, we 

 are reduced to the latter kind of evidence alone, if we except that which 

 may be derived from the fossil plants and the few fossil shells before 

 mentioned. 



"While we seem warranted in assuming that the strata in question, of 

 the IMiddle Park region, are really equivalent wdth the Laramie Group 

 of the Upper Missomi, the great Green liiver Basin, and of the plains 

 at the eastern base of the Eocky Moimtaius, the following comparisons 

 are of interest. 



The strata in question have an aggregate thickness in Middle Park 



