Douglass : A Geological Reconnaissance. 229 



Beyond these lie dome shaped hills which have not yet been reduced 

 to the level of the prairie. 



The reason why White Butte has a different appearance from the 

 surrounding buttes, was very apparent on closer examination. On 

 ascending the butte, the first rock examined was brownish gray sand- 

 stone. In places this contains impressions of leaves. Still higher is a 

 layer of sandstone which has a foliate, and, in some places, a concen- 

 tric structure. Above this, perhaps one hundred and fifty feet in 

 thickness, are beds of clay and sand, the greater portion of which are 

 almost white. In places these deposits contain much gravel. Where 

 the fine and coarse materials are mixed and show cross-bedding, it 

 strongly suggests a delta deposit. The principal portion of the deposit 

 is gray and white, the pebbles are of different colors, brown prevailing. 

 Though the color of this deposit, its texture, and the material of which 

 it is composed are different from that which prevails in the Fort Union 

 formation, yet I thought possibly that this formation might be the 

 same as the gray beds which are exposed beneath the sandstone cap 

 at Black Butte, though much thickened. But, when the vertebrae 

 of a large mammal were found, it was apparent that the formation 

 did not belong to the Fort Union. Later investigation showed that 

 it is undoubtedly Lower White River. The locality is interesting, 

 as the Tertiary is in contact with the lignite. The fact that the 

 northern end of White Butte is composed of two formations, explains 

 the difference which had been observed between the base and the top 

 of the butte; the former is Lower Tertiary (Fort Union), and the 

 latter Later Tertiary (White River). The deposits were therefore 

 made at widely separated intervals of time, and probably under very 

 different circumstances. In the lower portion of the White River 

 beds there are sandstones, hard in places, which weather into irregular 

 forms. There are also many brown ironstone concretions. The steep 

 slopes are difficult to travel over, as, when dry, the clay hardens and 

 the silicious sand and pebbles make the footing insecure. In places a 

 white soapy clay has been washed out of the beds into the little gullies 

 or ravines and has been covered with white sand. The clay holds the 

 water and remains soft underneath. If a heavy animal, like a horse, 

 steps on one of these places, even though there may be a dry sand-bar 

 or gravel-bar on top, he is apt to sink in up to the body. By digging 

 through the flat sand-bars in these little water-courses one gets water 

 which is sweet and refreshing, and, so far as my experience goes, it does 



