212 DESCRIPTIVE GEOLOGY. 



steps or terraces, the first of which is formed of the wliitish clays and sand- 

 rocks abeady mentioned as extending parallel to the line of the railroad 

 toward Washakie Station. About 4 miles south of these, a second line of 

 bluffs of greater elevation is composed of the striped red beds of the Upper 

 Vermillion Creek series. To this we have given the name of Cathedral 

 Bluffs, on account of the remarkable buttress-like forms into which their 

 faces have been weathered. A thickness of about 6 (JO feet of these pecu- 

 liarly-variegated beds is here exposed, composed of fine clays of red, green- 

 ish, and purple colors, with a varying admixture of fine white sand. These 

 are capped by about 100 to 150 f?et, of an impure concretionary limestone 

 of drab color, having at its summit a seam about 4 inches in thickness, of 

 oolitic limestone, which has been, in a great measure, silicified, and changed 

 into a dark-gray chalcedony. These upper calcareous beds represent the 

 base of the Green River group. The oolitic seam is made up of rounded 

 grains from one-thirtieth to one-tenth of an inch in diameter, of a -concentric 

 structure, cemented by a crypto-crystalline limy matrix. Examined under 

 the microscope, they show no evidence of organic origin, and are seen to be 

 almost identical with the limy sands, which are found on the present beaches 

 of the Great Salt Lake. A partial analysis of the agatized portion of this 

 seam gave 74.818 per cent, of silica, the remainder being principally car- 

 bonate of lime, with some alumina, oxide of iron, and magnesia. ■ The beds 

 of Cathedral Blufi"s have a dip of 3° to 4*^ to the southward, while the sur- 

 face of the plateau summit of the bluffs slopes off at a somewhat steeper 

 angle, so that, in the depressions of the dry water-courses to the south, the 

 underlying red beds have been exposed by denudation. 



Westward from Cathedral Bluffs, as far as Table Eock, extends a less 

 well-defined line of bluffs whose upper beds contain generally some calca- 

 reous layers, which are considered to be characteristic of the Green River 

 formation. Table Rock itself is made up of sandstones, and sandy and 

 calcareous shales, with some lignitic seams, and several thin beds of lime- 

 stone almost completely made up of fresh-water fossils, Melania, Vivi- 

 parus, and Unio, together with the agatized oolitic seam already observed 

 in Cathedral Bluffs. Only a thickness of about 500 feet of recognizable 

 beds is exposed in its cliffs, the base rocks being concealed by debris. The 



