eeduch.] SOUTHERN AREA GREEN RIVER GROUP. 131 



longing to this group, and we therefore find the Wasatch exposed for a 

 number of miles upstream. Eastward the Green River makes a sharp 

 turn and passes north of Essex Mountain. It there shows a very small 

 southwesterly dip; continuing northward we find the group tinning out 

 very decidedly. It extends up to Station 21, overlying Wasatch. This 

 point may essentially be regarded as its northeastern termination. From 

 there the northern line of outcrop runs in a direction south of west, and the 

 eastern one about southeast. Remnants of Green River beds are left 

 on the Wasatch at several places, showing that the group at one time 

 covered a much more extensive area. 



In this section of our district the lower members of the group are com- 

 posed of gray and bluish shales, more or less calcareous and arenaceous. 

 Higher up we find yellow and light brown shales, mostly very sandy, 

 but containing strata of impure, argillaceous limestones. Above these 

 follow concretionary sandstones and shales, of yellow and rusty brown 

 color. The former contain one very prominent horizon of siliceous ma- 

 terial, appearing in the form of chalcedony and agate. Near the base a 

 thin stratum of oolite was found. It shows the single grains of con- 

 centric structure firmly cemented by quartz. Another similar bed was 

 observed higher up in the shales, where the oolite was associated with 

 large quantities of silicified wood. Emmons has found* a similar oc- 

 currence of oolite near the base of the Green River series at a locality 

 south of Red Desert Station. It varies somewhat in character from that 

 which we observed, being of a gray color and containing calcium car- 

 bonate. The specimens we found are red, brown, and yellow, and silici- 

 fied throughout. It was observed about 28 miles west of north of Red 

 Desert Station. The higher horizon was noticed on Station 21. It 

 does not appear that the band extends for any considerable horizontal 

 distance. Near the base of the series we find the characteristic deposits 

 which have been designated as "paper shales." It is probably not in- 

 tended that this term should be synonymous with the German " Papp- 

 deckelrftchiefer" (pasteboard slates), but in point of fact the latter variety 

 does here occur. They are composed of extremely thin, tough lamina 1 , 

 which exfoliate upon exposure. In this condition they closely resemble 

 pasteboard which has been soaked in water. Both when compact and 

 decomposed, they are more or .less flexible. Mainly calcium carbonate, 

 aluminium silicate, and minute grains of clear quartz compose them. 

 Frequently they are bituminous, sometimes sufficiently so to burn. As- 

 sociated with these peculiar shales we found numerous banks of "cone- 

 in-cone" (Nagel-Kdllc of Germans). Their horizon is about 350 feet above 

 the base of the group. Together with them, and a little higher up, re- 

 mains of fishes were observed. Unfortunately the shales were there 

 (north of Mount Essex) so thoroughly decomposed and disintegrated 

 that no good specimens could be obtained. 



It has been mentioned in previous pages that the Green River Group 

 shows a general thinning out toward the north. Not only do the lower 

 shales decrease in vertical dimensions, but the upper sandstones become 

 very much thinner. West of Packer's Creek we find the total thickness 

 of the Green River series to be 1,700 to 1,800 feet. Of these the upper 

 sandstones with their shales occupy about 800 to 900 feet, and the arena- 

 ceous beds near the base about 150 to 200. This leaves an average thick- 

 ness of 700 to 800 feet for the shales. Approaching the northern termi- 

 nation of the group its total thickness amounts only to about 1,200 feet; 

 100 to 150 feet of lower sandstones and arenaceous shales, 050 to 700 



*Geol. ExpL Fortieth Par., vol. ii, 1877, p. 212. 



