5 o8 A. G. LEONARD 



Fort Union Formation 

 Character of the beds 

 Coal 

 Plants 



Invertebrates 

 Vertebrates 



White River Beds 

 White Butte area 

 Little Bad Lands area 

 Sentinel Butte area 

 Long Pine Hills area 



INTRODUCTION 



The Cretaceous formations represented in the area under dis- 

 cussion are the Pierre shale and Fox Hills sandstone. Overlying 

 the latter is a non-marine formation, which has variously been 

 called "the Ceratops beds," "Lower Fort Union," "Somber beds," 

 "Laramie," "Hell Creek beds," and "Lance formation." The 

 United States Geological Survey has recently adopted the name 

 "Lance formation," derived from the term "Lance Creek beds," 

 which was applied to the deposits by J. B. Hatcher, and this name 

 is employed in the following pages. The age of the Lance formation 

 is still unsettled, some geologists regarding it as part of the Fort 

 Union and thus early Eocene in age, while others believe that it 

 included, or is part of the Laramie and is, therefore, Cretaceous. 

 The Tertiary formations are represented by the Fort Union and 

 White River. 



Western North Dakota is particularly favorable for the study 

 of these formations, since they are excellently exposed in the 

 Little Missouri badlands and along the valley of the Missouri 

 and its tributaries. Bowman and Billings counties afford a con- 

 tinuous section extending from the Pierre shale up through the 

 Fox Hills, Lance formation, and Fort Union to the White River 

 beds of the Oligocene, involving a thickness of some 2,150 feet of 

 strata. 



The data here presented were gathered during seven seasons 

 of field work in North Dakota and Montana, a portion of the time 

 as assistant on the United States Geological Survey, and a portion 



