214 DESCRIPTIVE GEOLOGY. 



but their best exposures are hi the bluffs to the eastward, where they strike 

 north 30° east, with a dip of 4° to the southeast. Interstratitied with these 

 cak'-areous shales are thin seams of arenaceous shales, which seem to increase 

 proportionately as one ascends geologically ; the higher beds to the south of 

 the springs showing only outcrops of sandy shales and coarse, buff sand- 

 stones, which frequently contain rude casts of Unio. Occasional exposures 

 of these southerly-dipping sandstone beds are found along the bed of Bitter 

 Creek, above the springs, as far as its head. To the south of this is an open 

 plain country, in which no outcrops are found for a distance of 8 or 10 

 miles, but which is evidently covered by debris of the Bridger beds of the 

 Washakie Basin, which extend up on to the flanks of the bluffs formed by 

 the beds of the Green River series. 



To the east of the head of Bitter Creek, in the region of the old stage- 

 road, as far as Barrel Springs, extends a region of low, broken ridges, whose 

 beds dip slightly to the south, presenting bluff exposures to the north, 

 and made up mainly of sandstones and calcareous shales, which have been 

 referred to the horizon of the Green River series. At the southeastern point 

 of the Cathedral Bluff Plateau, the striped clay beds of the Upper Vermil- 

 lion Creek series are overlaid by about 200 feet of soft, light-colored lime- 

 stones and marls, which are capped by a thin seam of chalcedony, made up 

 almost entirely of casts of Goniohasis, whose form is very perfectly preserved. 

 This seam probably corresponds in geological horizon to the fossiliferous 

 limestones found south of Table Mountain. The local replacement of the 

 calcareous material by chalcedony, probably the result of chemical trans- 

 formation by soluble silicates, is a phenomenon of very common occurrence 

 throughout all these Tertiary beds. The strata which immediately overlie 

 these beds are concealed beneath the detrital accumulation and the wash of 

 the dry stream-beds to the south of Cathedral Bluffs. 



Along the stage-road, near Barrel Springs, are exposures of shaly beds, 

 which seem to correspond to the horizon of the calcareous shales found at 

 Bitter Creek. In the low ridges adjoining these springs are beds of thin 

 white calcareous shales, with a considerable development of carbonaceous 

 material, interstratitied with arenaceous beds. The beds are too much dis- 

 integrated to afford any continuous exposures, but seem to have abounded 



