CENTEAL AND EASTEEN IJTEVADA. 331 



result of solfataric action. At the foot of a northeastern spur of Prometheus, 

 on the western edge of the basm, is found another partially decomposed vari- 

 ety, of white color, having small crystals of quartz disseminated through the 

 feldspathic matrix. 



The line of fissure of this rhyolite eruption, as has been seen, is about 

 north and south ; the southern portion of the body, or that which occurs in 

 the slates, has a different character from the rock of Prometheus, which has 

 broken through the granite, and is, by the occurrence of granite on the pass 

 above Austin, isolated from the rest. There is no evidence to show that 

 these rocks are cotemporaneous or the reverse, since they are not found in 

 contact on the surface ; whatever the origin of the more southern rocks, how- 

 ever, the summit of Prometheus evidently marks the vent through which the 

 rocks, composing its slopes, have come to the surface. 



The most productive veins in the district occur on the south slope of 

 Lander Hill, the granite spur, which extends to the westward from Mount Pro- 

 metheus; of those most extensively explored the majority have a northwest 

 strike, and dip at a low angle into the hill to the northeast. In these veins 

 has been found a system of fractures or faulting, in a north and south direc- 

 tion, occurring with such regularity and persistence as to suggest the idea 

 that the surface of the spur has experienced a general downward movement 

 to the westward, or, what seems more probable, that the interior core of the 

 spur has been uplifted in the opposite direction, possibly at the time of the 

 rhyolitic eruption of Mount Prometheus, the hne of movement being generally 

 parallel to this fissure. 



In the upper part of Marshall's Carton, forming a dike in the granite, is 

 a dark-green, fine-grained rock, impregnated with iron pyrites, which re- 

 sembles a syenite, though its grain is too close to determine with accuracy its 

 mineralogical composition. To the south the granite body gradually grows nar- 

 rower, and in Ely's Canon, the fourth south from Austin, is no longer seen. 

 Here are hmestone-shales, generally dipping south and east, though their strikes 

 seem to vary a good deal. In the next canon south is the commencement of 

 a body of blue hmestone, which extends south as far as Big Creek, and seems 

 to be the least altered of any in the range. In it were found a few indistinct 

 molds of' fossils, but it is generally rather granular and crossed by small 



