KNi^Licii.] SOUTHERN AREA ERUPTIVES. 133 



occur near the base. Stratification is not very api>arent in it. At some 

 ])oints, wliere the granites of the h)wer range form gaps, the white, chalk- 

 like bluffs extend southward for a short distance. So far as could be 

 determined, they arc unconformable with the Green IMver series, which 

 tiiey Join along the Little Sandy Oreek. At some points the imperfectly 

 defined strata of this Pliocene series show a dip of 2^ and 3° to the 

 northeast. About 5 miles east of the Little Sandy it ends, very near 

 South Pass. It seems as if portions of it had formerly extended farther 

 east and south, but had been removed by erosion. No fossils were found, 

 but some specimens of a small Pupa. At no place do we tind a favora- 

 ble' section of the group, and an estimate of its thickness is therefore 

 necessarily not very reliable. I regard it as about 300 feet. 



Wyoming conglometxite. 



"Wherever we find Tertiary strata which have been but little disturbed 

 by subsequent erosion, we observe extensive deposits of this loose, irreg- 

 ular (!on glomerate. Along the southern slope of the SAveetwater Mount- 

 ains it is Aery abundant, totally obscuring the junction lines of the 

 <litferent groups. On the summit of Station 21 it is found as a small 

 renniant, about 12 feet in thickness, forming the A^ery highest point. 

 Indians liad here built up a small "lookout" Avith the bowlders. Xow 

 this is disturbed, as our monument occupies its place. L^pon the sum- 

 mits of some of the higher Tertiary hills this conglomerate attbrds the 

 only material for such purj)oses, as the strata AA'eather into small frag- 

 ments, leaA ing no bowlders of sufficient size. Table Hills and Steam- 

 boat liuttes, a little farther Avest, are covered with the same material. 

 At these j)laces some of the metamorphic bowlders are so large that 

 they raay have been and probably were transported by ice. Within the 

 Pliocene A^alley west of South Pass the same conglomerate occurs in 

 abundance. It is scattered to a greater or less extent all OAcr the coun- 

 try Avhich has been subjected to extensiA^e erosion. HaAing been removed 

 fi-om the regions AA'here it Avas first deposited, it was dropped in the di- 

 rection taken by the Avaters which so greatly modified the surface of the 

 country. Although our observations are somewhat imperfect on account 

 of the erosion folloAving the regular deposition of Tertiary groups, I am 

 inclined to regartl the maximum accumidation of this conglomerate as 

 oceiuTing along the shores of the former Tertiary lakes. 



ERUPTIVES. 



IMention has been made of the eruptiA^es which form a series of hills 

 and blulis north and northeast of Salt Wells. Moimt Essex is the prin- 

 v,i\n\\ one of these. A high bluff is formed by volcanic material Avhich 

 has been ejected through the strata of the Wasatch Group. Sloping 

 gently to tiie noithAvard, AA^e find th it the summit is essentially a small 

 plateau, containing one proniinent, conical point. To the south and east 

 the mount aui presents A^ertical, rocky feces, Avhich surmount a steep, fur- 

 roAA'ed slope. The rock is dark gray to black, more or less vesicular, and 

 contains small crystals of augite and biotite. Immediately south of 

 Essex Mountain is a table-topped hill, Avhich on some maps is marked 

 as " Blijck Ijutte." Here the lava has escai^ed through a fissure trend- 

 ing about north 45^ west, and has covered the Wasatch beds Avith about 

 400 feet of black ro{;k. It is somcAvhat columnar, and ])r(!sents a nearly 

 verticiil face on all sides. West of Essex Mountain, on the drainage of 

 Packer's Creek, is an isolated needle of basalt, known as IJock Point* 



