PENN oaKok 597 



referred to the Upper Coal-Measure group, though no fossils were obtained 

 from them. Their structure is shown in the upper section of tlie map. 



In Penn Canon, which is cut at right angles to the strike, nearly- 

 through the range, a thickness of some 3,000 to 4,000 feet of the beds of the 

 Weber Quartzite is exposed. The structure is much obscured, but seems to 

 be generally that of an anticlinal, whose eastern member is very steep and 

 nearly perpendicular, while the main body of the range is formed of westerly- 

 dipping beds, whose angle in the centre of the range is only about 10°, 

 steepening to 25° on the extreme western foot-hills. The lowest beds ex- 

 posed show a considerable thickness of black argillaceous shales and quartz- 

 ites, which are overlaid by conglomerates, generally including a certain pro- 

 portion of angular, cherty fragments, while the most prominent beds are the 

 peculiar dark quartzitic sandstones already mentioned, which here are coir 

 ored by hydra ted oxide of iron. Microscopical examination shows that in 

 both the quartzitic sandstones and conglomerates, the quartz-grains contain 

 a great number of fluid-inclusions, and also small laminae of mica, some- 

 times of distinctly hexagonal form. This fact also points to some pre- 

 existing uplift of crystalline rocks, from whose debris these were formed, 

 which is now worn awav, or concealed beneath the later formations. In 

 the upper portion of the series is an included bed of limestone, underlying 

 the upper conglomerate. 



Immediately north of the canon, the spurs are capped by a red porphy- 

 ritic rhyolite of a type which is very widely spread throughout Nevada. It 

 has a reddish-purple, compact, felsitic groundmass, and contains small crys- 

 tals of sanidin and quartz, with a little hornblende and occasional flakes of 

 black mica. It has a peculiar irregular fracture, and in a hand-specimen, but 

 for the presence of quartz, might be easily taken for a trachyte. To the south 

 of Penn Canon, the range consists of low, rather broken hills, whose structure 

 is masked by detrital material, but which, as far as observed, were composed 

 principally of the greenish conglomerates and quartzite sandstones of the 

 Weber group, having a prevailing dip of 10° to the westward. 



On the western slopes of the range, toward Susan Creek, are light- 

 gray rhyolitic tufas, similar to those north of the coal-mines, being rather 

 porous, and containing a few scattered crystals of feldspar and quartz in a 



