KXDLicH.l SOUTHERN AREA GREEN RIVER GROUP. 131 



loiiiiiiig" to tliis ftioiip, and ^vo therefore find the Wnsatch exijoscd for a 

 nnmber of miles uj)stic';nn. EastWiU'd the Green Kiver makes a sharj) 

 turn and ])as.se;i nortli of Essex Monnlain. It there sliows ;i very small 

 sonth westerly di]); eontinninj;' northward we tind the gronj) thininii' out 

 very deeidedly. It extends n]) to Station 21, overlyinj;- Wasatch. This 

 point r.ia.y essentially be re.^arded as its northeastern t(H'mination. From 

 there the northern line of outeroj) rnns in a direction sonth of west, and the 

 eastern one about southeast. IJemnauts of Green Iiiver beds are left 

 on the Wasatch a<t several phices, showhig that the group at one time 

 covered a much more extensive jirea. 



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 ui> v.e lind yellow and bght 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 ba.se a 

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

 centric sti'ucture hrndy cemented by quartz. Another similar bed v/as 

 observed higher up in the shales, where the oolite was associated v.ith 

 large <pi;nitities of siliciiied wood. Emmons has found* a similar oc- 

 currence of 0()lite near the base of the Green River series at a locality 

 south of lied Desert Station. It varies somewiiatin character ihmi that 

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

 bontite. The s.i)ecimens we found are red, brown, and yelloAA^, and silici- 

 iied throughout. It was observed about 28 miles Avest of north of I'ed 

 De:-,ert 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 Ave tind the characteristic depo. its 

 which have been designated as "i)aper shales." It is probably not in- 

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

 decud-k'cliiefet''''' (pasteboard slates), but in point of fact the latter variety 

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

 Vv'hich exfoliate ui>oii exposure. In this condition they closely resemble 

 par'.teboard Avhich has been soaked in Avater. Both Avlien conipiict 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 Avith these peculiar shales aa^c found numerous banks of " cone- 

 iu-cone" {N'afjel-KalJc of Germans). Their horizon is about 350 feet above 

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

 mains of lishes Avere obserA^ed. Unfortunately the shales Avere 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 

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

 shales decrease in A^ertical dimensions, but the upjier sandstoncjs become 

 very much thinner. T¥est of Packer's Creek Ave tind the total thickness' 

 of the Green EiA'er series to be 1,700 to 1,800 feet. Of these the ui)i)er 

 sandstones with their shales occu])y about 800 to 000 feet, and the arena- 

 ceous beds near the base about 150 to 200. This leaA'es an aA'era.ge thick- 

 ness of 700 to 800 feet for the shales. Approaching thcnorthc rn 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. 



