170 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



of the Cretaceous. All the sediments are more or less impure sandstones, 

 and even those characterized by argillaceous deposits are usually sandy. 

 While the organic forms found here may be such as occur elsewhere in the 

 Colorado shales, they are also forms that extend upward into the sandstones 

 of the Montana. These arenaceous shales are well developed in the valley 

 of Lizard Creek, and along- the east side of the stream are exposed in a 

 number of localities above the stream bed. From them have been obtained 

 Ostrea, Anomia, Inoceramus, and the widely distributed middle Cretaceous 

 species, Cardium pauperculum. 



Beds similar in lithological habit are exposed in the valley to the west- 

 ward, which in its topographic outline closely resembles Lizard Creek, and 

 still farther westward these rusty sandstones crop out from beneath thin 

 cappings of rhyolite at a number of localities on both sides of the Snake 

 River trail. One such exposure is seen along the trail not far from where it 

 crosses the summit of the spur which extends westward to Snake River. 

 On the east side of the river, opposite the mouth of Berry Creek, a small 

 exposure of sandstone and shale occurs, striking nearly due east and west 

 and dipping north. 



Owing to the limited area exposed and the fact that the surrounding 

 country is mainly covered by drift the outcrop is not indicated on the 

 map. According to Prof. J. P. Iddings, this sandstone carries a seam of coal 

 4 inches in thickness. Northward, and on the extreme western spur of the 

 ridge, the sandstones and shales are exposed, extending up the hill slope for 

 several hundred feet. Here they strike northeast and soutlrwest, with a 

 dip of 25° NW. It is possible these beds belong to the Colorado forma- 

 tion, but in the absence of all organic remains they have been placed in the 

 Montana, together with other beds of similar lithological character found 

 in this region. 



Huckleberry Mountain. — The central mass of this group of mountains has 

 been designated Huckleberry Mountain. Its summit is formed of a broad 

 sheet of rhyolite, slightly inclined toward the south. On nearly all sides 

 this rhyolite capping rises above the underlying rocks as an abrupt wall, 

 which along the east side forms an escarpment over 100 feet in height. 

 This east wall limits the rhyolite in this direction, and the entire eastern 

 slope of the mountain, down to Coulter Creek, exposes only strata of the 

 Montana formation. The beds dip at low angles to the southeast. Beneath 



