184 T. W. Stantmi — Foa' lUlh Sandstone. 



ail oyster bed iinist have been formed in tidal waters connected 

 with the sea, and its presence here argues strongly for the 

 assumjitioii that the underlying portion of the Lance formation 

 was formed near sea level so that a slight downward movement 

 permitted local teiiiporaiT admission of brackish water into 

 the low lying swamps and marshes in which coal was forming. 

 It is, therefore, most probable that the abrupt change from 

 marine to fresh-water and land conditions seen near Marmarth 

 is purely local, and that the eroded surface at the top of the Fox 

 Hills does not represent a time interval of any geologic 

 importance. 



Lance Creek Area, Converse County, Wyoming. 



This well-known area has been described by Hatcher* awd 

 by Stanton and Knowlton,f and has recently been further 

 discussed by Knowlton;}: and Stanton. § In the examination of 

 last summer special attention was given to the Fox Hills sand 

 stone and its relation with the basal portion of the Lance forma- 

 tion. Our principal contribution to the knowledge of the 

 stratigraphy of the area was the discovery that the marine 

 Fox Hills deposits extend about 400 feet higher than had pre- 

 viously been determined, and that non-marine coal-forming 

 conditions were temporarily inaugurated here before the close 

 of Fox Hills time. 



The first section examined is on the south side of Cheyenne 

 River at the mouth of Lance Creek, and extending up the 

 creek a mile and a half or two miles. Beginning at the top of 

 a prominent white sandstone the section is as follows : 



Feet 



1. White cross-bedded sandstone with irregular brown indu- 



rated bands, masses, and concretions 50 



2. Soft sandy shale with bands of lignitic shale. Fragments 



of dinosaur bone were found on the surface here 50 



3. Sandy shale full of Corhicula cytheriforniis ? and Corhi- 



cula suhdliptica var. moreauensis ... 1/ 2-1 



4. More or less carbonaceous shale 15 



5. Soft massive gray sandstone with many brown concretions 25 



6. Gray sandstone and sandy shale with bands of sandstone 



containing Fox Hills fossils, about — . 150 



1. Cross-bedded, ripple marked, reddish brown sandstone 



with irregular base 8 to 10 



8. Massive soft buff sandstone with many large concretions 



and indurated masses and an abundant Fox Hills fauna. 100 



9. Pierre sliale with only the top exposed . 



* This Journal (3), vol. xlv, pp. 135-144, 1893. Am. Naturalist, vol. xxx, 

 pp. 112-120, 1896. f Bull. Geol. Soc. Am., vol. viii, pp. 128-137, 1897. 

 :t:Proc. Washington Acad. Sci., vol. xi, pp. 179-238, 1909. 

 glbid., pp. 239-293. 



