OCT 



PROCEEDINGS 



OF THE 



AJ^ERICAN PHILOSOPHICAL SOCIETY 



HELD AT PiniADELPflli FOR PROMOTING USEFUL KNOWLEDGE. 



Vol. XLI. April, 1902. No. 170. 



A CRETACEOUS AND LOWER TERTIARY SECTION 

 IN SOUTH CENTRAL MONTANA. 



(Plate XXIX.) 

 BY EARL DOUGLASS. 

 {Read April S, 1902.) 



This paper is intended only as a preliminary report of an inter- 

 esting geological section — an account of what has been done and a 

 suggestion of what is yet to be accomplished. The points of inter- 

 est are: (i) The completeness of the Upper Cretaceous which 

 overlies the older beds, probably Jurassic and Lower Cretaceous, 

 and underlies the Fort Union, which here contains mammalian 

 remains, correlating it with the Torrejon of New Mexico; (2) the 

 excellent exposures of the strata, giving a good opportunity for 

 study; and (3) the occurrence of interesting fossils, especially verte- 

 brates, in several different horizons. 



The region here referred to lies east of the Crazy Mountains and 

 south of the Big Snowies, in the basin of the Musselshell River, in 

 Sweetgrass County. It extends from south of the Musselshell River 

 southward twelve or fifteen miles, and eastward from a line passing 

 southward from Harlowton on the Musselshell about the same dis- 

 tance. This is part of the south limb of a broad anticline, the 

 general trend of which is south of east. This anticline is dissected 

 longitudinally by the Musselshell. The lowest strata exposed are 

 upheaved into a dome-shaped uplift southeast of Harlowton and 

 four or five miles south of the river, where strata which are appar- 

 ently of Jurassic age are exposed. 



This region is on the western border of the elevated plains coun- 

 try, and occupies a position intermediate between the plains and 



PEOC. AMER. PHILOS. SOC. XLI. 170. N. PRINTED AUG. 29, 1902. 



