l8o KNOWLTON 



9. Glendive, Montana, to Medora, North Dakota 199 



10. Bismarck, North Dakota, and vicinity 200 



11. Yule, Billings County, North Dakota, and vicinity 201 



12. Probable area in Northwestern South Dakota 202 



13. Weston County, Wyoming, area 203 



14. Northward extension of AVeston County area to connect with 



Miles City area 2 04 



15. Converse County, Wyoming, area 205 



16. Area to the eastward of the Bighorn Mountains, Wyoming 209 



1 7 . Bighorn Basin, Wyoming 212 



18. Probable distribution of lower Fort Union in other areas 215 



Relations between the lower member of the Fort Union and underlying 



formations 216 



Relations between lower and upper members of Fort Union 217 



Stratigraphic relations of the lower member of the Fort Union to the 



Laramie 217 



Paleontological characters of the lower Fort Union: 218 



1. Plants 218 



a. Plants identified in lower Fort Union 219 



b. Paleobotanical proof of the Eocene age of the Fort Union 



flora 224 



2. Invertebrate evidence 226 



3. Vertebrate evidence 229 



a. Dinosaurs 229 



b. Mammals 233 



c. Chelonians 235 



d. Fishes 236 



Line between Cretaceous and Tertiary 236 



Summary and conclusions 237 



Introduction. 

 problem and conclusion. 



The present paper deals with the extensive series of fresh-water 

 deposits of the northwest {i. e., broadly, the region east of the Rocky 

 Mountains and between Wyoming and the valley of the Mac- 

 kenzie River) comprising what is here considered as the Fort Union 

 formation. It is shown that the Fort Union embraces more than 

 has been commonly assigned to it. Conformably below the beds by 

 some geologists considered as the true Fort Union occur dark-colored 

 sandstones, clays and shales, which have often been incorrectly 

 referred to the Laramie, or its equivalent, but which are stratigraph- 

 ically and paleontologically distinct from the Laramie, and the con- 

 tention is here made that these beds, which include the " Hell Creek 



