180 KEPORT UNITED STATES GEOLOGICAL SURVEY. 



has been reported from the marine Cretaceous strata of the Fox Hills 

 Group at several points west of the Rocky Mountains. Regarding it 

 provisionally as a Laramie ibssil of course implies the reference of the 

 stratum containing it east of the mountains to the Laramie Group, which 

 Dr. Hayden has usually regarded as the lower stratum of the Lignitic 

 series ; but as the sedimentation was evidently continuous from the lower 

 to the upper of these groups, he is understood to have selected that 

 stratum as approximately upon the plane of demarcation between them. 

 This fucoicl is quite abundant at the Saint Trains locality. 



2. Fossil wood. 



Fragments of fossilized exogenous wood are somewhat commonly met 

 with in these Cretaceous strata, both in the form of comminuted carbon- 

 ized material, and that of pieces of wood which, although mineralized, 

 still retain much of the original texture and aspect. In the latter con- 

 dition it is not unfrequently found to have been bored by a species of 

 Teredo. 



3. Ostrea patina Meek & Hayden? 



A few scattered shells of an Ostrea were found among the other fos- 

 sils at Fossil Eidge, which probably belong to this species, which was 

 originally described from the Fort Pierre Group of the Upper Missouri 

 River region. The species of this genus are too variable, and the speci- 

 mens in question too few to allow of positive specific identification, 

 besides which 0. patina is an unusually variable species. 



4. Pteria Mydeni Hall & Meek. 



Dr. Hayden originally discovered this species in the vicinity of Fort 

 Pierre, on the Upper Missouri River, near the base of the Fort Pierre 

 Group, and with the present exception, so far as I am aware, it has not 

 been found elsewhere. A single valve only was found at the mouth of 

 the Saint Yrains, but it seems to be identical with the species here 

 named. The original description and figure given by Hall and Meek are 

 copied in vol. ix of the United States Geological Survey. 



5. Pteria linguiformis Evans & Shumard. 



This is nowhere a very abundant species, but it is one of the most 

 widely distributed of those which characterize the Cretaceous strata of 

 the West. It occurs on both sides of the Rocky Mountains, but I ob- 

 tained it myself only at Fossil Ridge, in the district under discussion. 

 It is also known to range through both the Fort Pierre and Fox Hills 

 Groups of the Upper Missouri River region, where it was first discovered. 

 This species is very like the Avicula nitida of Forbes, from the Creta- 

 ceous rocks of Southern India ; but it is not my purpose in this connec- 

 tion to discuss questions of identity of these species, except so far as 

 relates to the equivalency of the strata in which I found them with other 

 Cretaceous strata of North America. 



6. Pteria (Oxytoma) nebrascana Evans & Shumard. 



This is also a widely-distributed and often abundant species, being 

 found in both the Fort Pierre and Fox Hills Groups of the Upper Mis- 

 souri River region, and also having been discovered far up in British 

 America. It was found abundantly, but not very well preserved, in a 

 thin, soft, sandy, and clayey layer near Frank Marck's farm, five miles 

 west of Greeley. 



