180 T. W.Stanton — Fox Hills Sandstone. 



59G9. Sec. 27, T. 14 N., R. 1!) E. Soutli side of Moreau River, 

 above Tluiiuier Butte P. O. 



Corbicula nebrascensis M. & II. 

 Melania inscnlpta Meek 



* Scaphites conradi var. intermedins Meek 



* IScajjhites cheyenneiisis (Owen) 



The section in wliich tiiis collection was obtained is described 

 on p. 176. 



5975. North side of Thunder Butte Creek near south line Sec. 12, 

 T. 15 N., R. 18 E. 



Ostrea glabra M. & H. 

 Anomia iidcronema Meek 



Corbicula occidentalis M. <fe H. , 



Corbicula ci/theriforrnis M. & II. 

 Corbicula subelliptica var. rnoreauensis M. & H. 



* Tancredia americana M. & H. 



* Tancredia ? n. sp. 



* Lunatia subcrassa M. & H. ? 

 Melampus sp. 



Melania loyomingensis Meek 

 Melania insculpta Meek 



* iSca^Jhites conradi (Morton) 



The section at this locality is described on p. 175. 



The brackish-water species elsewliere are found in the 

 Laramie and in the non-marine formations of the Montana 

 group, but the marine forms, especially the ammonoids, which 

 give the best evidence as to age, belong to the Fox Hills fauna. 

 It is clear from these occurrences that there was no erosion 

 interval of any geological importance between the marine Fox 

 Hills and the overlying brackish-water bed, and that the latter 

 belongs to the Fox Hills epoch of sedimentation. 



Above the brackish-water horizon is the fresh-water Lance 

 formation consisting of soft sandstones, shales, thin coals and 

 carbonaceous shales, retaining the same general character 

 through 500 or 600 feet of strata. The flora from these beds, 

 ranging from the bottom to tlie top, is referred by Dr. Knowl- 

 ton to the Fort L^nion. Vertebrate fossils are common, espe- 

 cially in the lower 100 feet and ranging down to the base. 

 These include the dinosaurs Triceratops and Trachodon with 

 several other genera that are charactei'istic of the Lance forma- 

 tion fauna elsewhere. 



The history of the epoch immediately following the Fox 

 Hills sedimentation in this region has received two very differ- 

 ent interpretations. One is the view here presented, that with- 

 out any unrepresented interval of importance there was gradual 

 transition from marine conditions through brackish-waters to 

 the land and fresh-water conditions that generally prevailed 

 during the deposition of the Lance formation. The other 



