WAH-WEAH RANGE. 567 



granite on all sides, except toward the valley, occurs a heavy body of 

 quartzite, which has been referred to the Ogden Devonian, although but 

 little examined. Throughout Kevada, where large bodies of quartzite are 

 found without any clue to their stratigraphical relations with an underlying 

 or overlying limestone, the adjacent rocks being either granites or Tertiary 

 volcanic outflows, it is exceedingly difficult, if not impossible, to definitely 

 determine their true geological horizons. In many cases, lithological and 

 structural resemblances will furnish a strong aid to such determinations, 

 which, when followed up, will not infrequently throw the evidence in favor 

 of one or the other of the great zones of quartzite ; but unfortunately, in 

 many cases, such resemblances are meagre, and the reference is made upon 

 theoretical grounds, based upon slight evidence, or even personal impres- 

 sions received in the field. The relation of the quartzite of the Wah-weah 

 Range to the heavy body of limestone of Robert's Peak has not been 

 worked out, but has been regarded as overlying it, and therefore has been 

 referred, as already mentioned, to the Ogden formation. Geologically, the 

 chief interest in the Wah-weah Range is found beyond the boundary of the 

 map, where the quartzites give out, and are replaced by immense flows of 

 trachyte and rhyolite, extending to the southern end of the range, and con- 

 cealing the lower sedimentary strata. In one or two places, however, the . 

 quartzite comes to the surface, indicating that the intrusive rocks follow, 

 as is so often the case, the longitudinal axis of the Palaeozoic uplift. 



Trachyte 'is the predominant rock, and forms the broad, table-like body 

 which extends the width of the range. A number of small hills and peaks 

 rise above the general level, and the mass is traversed by numerous deep 

 canons and ravines, exposing a great thickness of trachyte. It is, indeed, 

 the largest body of trachyte observed in Central Nevada. East of the 

 Virginia Range, trachyte outbursts are usually confined to narrow dikes, 

 isolated hills, or cappings of older beds; the broader areas of acidic rocks 

 being mostly of the rhyolitic variety. It would appear, however, probable 

 that many large fields of trachyte have been poured out, and have since 

 been buried beneath extensive flows of both rhyolite and basalt. It is also 

 worthy of note that this trachyte mass lies slightly inclined to the westward, 

 or toward the lower valley. 



