588 DESCRIPTIVE GEOLOGY. 



pal exposures are in the deep canons at the base of Carlin Peaks, where is 

 the greatest elevation of the range. Here, at the head of Annie Creek, was 

 found a considerable body of siliceous and green argillaceous slates, enclosed 

 in limestones having a westerly dip, while at the north of Carlin Peaks are 

 also some few exposures of dark-blue and gray limestones, which are also 

 seen at the gap of Maggie Creek, where, in direct contact with the rhyolite 

 overflow, one bed of limestone has become marbleized. These sedimentary 

 rocks, from which no palseontological evidence was obtained, have been re- 

 ferred, on grounds of general probability, to the Lower Coal-Measure group. 



At Carlin Peaks, the range has a distinct double crest, of which the east- 

 ern portion doubtless represents the original sedimentary elevation, while 

 the western crest is formed by a body of andesite, whose general direction is 

 suggested by the isolated exposures of andesite from a little north of Wagon 

 Canon to the western of the Carlin Peaks. The two more northern bodies 

 of andesite, that where the Emigrant Road crosses the range and that of the 

 western of the Carlin Peaks, diifer from the andesite found in Palisade 

 Canon, in containing some augite, and in having a more glassy base. They 

 resemble closely the augite-andesite of the Wachoe Mountains. 



That from the Emigrant Road is a quite porous rock, with prevailing 

 plagioclase, considerable sanidin-feldsjDar, and dark-brown hornblende, with 

 a good deal of yellowish, decomposed augite. Under the microscope, the 

 groundmass is seen to have something of the microlitic structure peculiar 

 to the augite-andesites, and many of the hornblendes are somewhat decom- 

 posed, and have the characteristic black border. 



The andesite from the head of Annie Creek is less porous. It is a 

 dark-gray compact rock, rich in hornblende, containing also a good deal of 

 yellowish-brown augite and some apatite. Under the microscope, the feld- 

 spars are seen to be mostly plagioclase, but with them are associated some 

 schistiform, monoclinic feldspars and the groundmass to have the felt-like 

 structure of augite-andesites. The feldspars are remarkable for containing 

 inclusions of yellow glass, with a thick bubble, as shown in Vol. VI, Plate 

 V, fig. 3. This andesite forms a considerable mountain mass, and rests 

 directly on the slates and limestones, while its flanks are covered by flows 

 of rhyolite. 



