216 DESCRIPTIVE GEOLOGY. 



compact siliceous material, and, where the heart of the tree has decayed out, 

 is loosely filled by crystalline quartz, still preserving some of the general fibre 

 of decayed wood. The position of the beds of this ridge, so high above the 

 surrounding country, and their apparent horizontality, might at first lead 

 one to suppose that they represented the highest portion of all the Tertiarie« 

 in this basin ; but a dip of only 2° would carry them 1,000 feet below the 

 surface in the centre of the Washakie Basin, whereas almost all the 

 observed dips, where the bedding was distinct enough to determine them, 

 were from 3° to 4° toward the centre. 



The region to the south of Haystack Mountain, and west of Washakie 

 Mountain, is occupied by a series of northwest and southeast ridges, formed 

 by the beds of the Bridger and Green River groups, in which, as seen from a 

 distance, erosion has cut sufficiently deep into the beds to give good exposures 

 of the rocks which compose them ; this region was not, however, traversed 

 by our parties. In the western portion of the Washakie Basin, the upper 

 beds of the Bridger series have been completely disintegrated, and have 

 left an open level country in which are no rock exposures. Along the bluff- 

 line, from Pine Bluffs southward, the calcareous beds of the Green River 

 series form the summit of the ridge, while the striped beds of the Vermillion 

 Creek group are exposed along the base, easily distinguishable by their 

 characteristic color. 



About 12 miles southeast from the head of Bitter Creek, to the east 

 of Pine Bluffs, the first exposures of the characteristic green clays and marls 

 of the upper beds of the Bridger group are met. After passing over a 

 level country covered with sand dunes, one comes suddenly upon a 

 series of infinitely branching ravines and gullies cut into the clay beds of this 

 group, with narrow trench-like ravines from 50 to 100 feet deep, and 

 often not more than 20 feet wide at the top, with perpendicular sides, 

 which show the characteristic scenery of the Tertiary bad-lands. From 

 here southwestward, this bad-land region extends to the dry stream-bed 

 to the north of Cherokee Ridge, ending in an irregular line of bluffs, 

 facing southward and. having a northeast direction, which present the most 

 remarkable forms of erosion. The characteristic rocks of this bad-land 

 country are a series of greenish-drab clays and marls more or less 



