228 Annals of the Carnegie Museum. 



beds exposed here, and to obtain detailed sections with accurate meas- 

 urements. Though there are vast exposures of lower beds, the higher 

 ones appear only in the butte. I was somewhat disappointed in not 

 finding in this whole series of beds any bones or teeth, which would 

 settle beyond dispute the question of the age of the formation. I do 

 not know that any one has denied that they are Fort Union, but 

 many have regarded the Fort Union, Great Lignite, and Laramie as 

 one formation ; others have maintained the Fort Union to be only a 

 division, or local phase, of the Laramie ; while still others believe the 

 Laramie and Fort Union to be distinct formations, the latter of con- 

 siderably later age than the former. Some of the bones, which had 

 been found on the Little Missouri Horse Ranch, had been sent to the 

 Smithsonian Institution, and they proved to be the bones of a bison, 

 probably an extinct species. 



From what had been seen and heard it was suspected that the White 

 Butte might represent a different formation from Black Butte. On 

 the seventh day of August I went to examine the former. On my 

 way I stopped at the house of Mr. T. F. Roberts, which is west of the 

 northern portion of the butte on the stage road from Medora to Sand 

 Creek postoffice. Looking southward from Mr. Robert's house, the 

 valley of Sand Creek appears as an undulating prairie-land, bounded 

 on the east by White Butte. On the west the valley is continuous 

 with the vast rolling prairie, which opens out to the westward ; but 

 on the south, narrowing and sloping gently upward, it extends 

 between the rudely conical, dome- and hog-back-shaped outliers of 

 Black Butte on the right, and White Butte on the left. The greatest 

 extent of Black Butte is nearly east and west, while that of White Butte 

 is east of south and west of north. In some places the gray banks of the 

 lignite beds are seen along Sand Creek, which has only a small surface 

 flow of water in dry weather. This stream issues from near the south 

 end of White Butte dissecting its western ridge. Partly on account 

 of the slope of the valley to the northward, the western ridge of White 

 Butte (Plate XVI) appears to decrease in height to the southward and 

 merge into the grassy plain. It is not flat on top, but is irregular in 

 outline, with low rounded prominences which are almost white. These 

 upper white beds terminate near the northern portion of the butte east 

 of the Robert's Ranch. Just north of this are lower flat-topped 

 mounds. Extending northward from these are lower benches and 

 mounds, and still farther north a large mound with a conical peak. 



