GEOLOCICAI, i;i:i'di;t. 331 



altered slates, much like roofing-slates. On the west side of the range dioritic and 

 trachytic porphyry prevails ; also pitchstone was found, and scattered knobs of such 

 recks extend across Butte Vallev, on the west side of which the hrown porphyry is 

 again prominent Near the southern route the ramre seems to he wholly composed of 

 very compact gray siliceous limestones, in which I found no fossils; hut from their 

 similarity to Devonian strata, farther west, I am inclined to consider them coeval. A 



Vallcv, is evidently composed of the yellow rocks of Upper Carboniferous a-e (see 

 below), of which a few doubtful traces were also noticed in the pass to Butte Valley. 

 This valley is closed at the south end by mountains of brown dioritic porphyry, and 

 rocks allied to the pitchstones, forming a spur of a great eruption, which has its center 

 south of "Summit Spring, in the next range, and covers a considerable area. 



On the northern route the divide between Butte Valley and Long Valley is low, 

 composed of porphyritic rocks and light-colored limestones. Part of these are light 

 gray, siliceous, and subcrvstalline, or" finely crystalline; others are light-yellowish, 

 areno-argillaceons, and have an uneven fracture. They are characterized, by a large 

 number of fossils, as an Upper Carboniferous formation/but differ much from the other 

 strata of that age, as developed farther east. 1 may refer to what has been said under 

 the head of Stratified Rocks, and to Mr. Meek's report. West of Long Valley we find 

 similar strata, continuing to the summit of the pass to Ruby Valley, where a blackish # 

 eruptive rock, which looks basaltic, but is perhaps allied to the greenstones, forms a 

 considerable protrusion. On the west side, in Murrv Canon, we have again the yel- 

 low rocks, but apparently more siliceous and slaty, and less fossiliferous. Their trend 

 and dip are variable, and I did not obtain a section, but the formation must attain a 

 thickness, at least, of several hundred feet. The strata of the spur of hills farther 

 north, in Ruby Valley, show the same color. A few fossils from the gray limestone 

 of an isolated low hill near the road, more resemble Lower Carboniferous types. 



On the southern route these light-gray and yellow limestones and slates form the 

 mountains between Butte and. Phelps Valleys, north of Summit Spring, south of 

 which they are cut off by the porphyries and allied rocks. In the low divide between 

 Phelps and Buell Valleys, and in some hills farther west, similar light-grayish and yel- 

 lowish rocks crop out. Some strata there are full of joints of the columns of Crinoldea, 

 and a few fossils from that point are considered by Mr. Meek as more like Lower Car- 

 division, it may perhaps exist. The presence of Devonian strata, a few miles farther 

 west, is favorable to the supposition that these beds occupy a lower position in the 

 Carboniferous series than those near Summit Spring. 



We cross the Humboldt Mountains on the northern route, near their southern 

 extremity, where their great elevation suddenly falls off, and minor ranges appear in 

 their stead. In this latitude the Humboldt Mountains appear to be made up of strati- 

 fied rocks from their base to the highest summits. I noticed blue and gray siliceous 

 limestones, also flint rock, and a coarse, partly conglomeratic sandstone, perhaps iden- 

 tical with the one in the next range west. These rocks belong probably to the Car- 

 boniferous and older formations. Only a small outcrop of feldspathic rock was observed 



