MONTEZUMA EANGE, 7(51 



southeast, and those on the opposite to the northwest. From the large 

 basahic field southward, for 8 miles, as far as Karnak, rhyolites form the 

 whole of the high summit of the range down to the plain on either side, 

 with the exception of a few limited outflows of basalt at the base. Here, 

 along the extreme foot-hills, and occasionally rising out of the Quaternary of 

 the valley, are a number of small basaltic hills and limited regions, cut by 

 interesting basaltic dikes, having a prevailing northwest and southeast 

 direction. 



About 2 miles up Bayless Caiion, there is exposed a series of siliceous 

 and argillaceous slates, of great thickness, having prevailing dark purplish- 

 blue and green colors, overlaid conformably by limestones roughly estimated 

 at 1,500 feet in thickness. The transition rocks are highly laminated, and 

 show frequent alternations between the siliceous and calcareous materials. 

 The strike of the sedimentary series is from north 38° to 40° west, with a 

 dip of 80° to the southwest. They extend northeastward, running out into 

 the plain in the region of Brown's Station, where they are broken through 

 by black basalts, which stand oat in isolated masses entirely separated from 

 the main fields of basalt. These beds, consisting of slates and limestones, 

 have been referred to the Jurassic from their lithological resemblance to the 

 slates and limestone known to be Jurassic, in the West Humboldt Range, 

 and from their similarity to certain California series. No fossils were found, 

 and it is by no means certain that the beds do not belong to the Triassic 

 formation, agreeing with those found upon the opposite side of the Hum- 

 boldt Valley. 



Directly above that part of Bayless Caiion which is occujDied by the 

 sedimentary strata, there occurs a rough broken country, out of which rise 

 a series of high eruptive ridges, exhibiting a variety of rhyolitic forms. 

 The highest and by far the most interesting part of this region is an exceed- 

 ingly sharp broken ridge trending approximately north and south, and 

 rising about 1,500 feet above the surrounding hills, and 3,000 feet above the 

 Humboldt Valley, to which the name of Karnak has been given, from its 

 resemblance to ruins. Along the crest of this ridge, the rhyolite forms a 

 series of clusters of prismatic columns of all sizes, from three feet down to an 

 inch in diameter. They show from three to seven sides, most frequently 



