468 QUrCKSILVEK DEPOSITS OF THE PACIFIC SLO]:'E. 



resembling a I . The great ore bodies are distributed along these two 

 fissures, making irregularly into the walls. The wedge between the fissures 

 also contains ore bodies. They are always accompanied by evidences of 

 motion and by a mass of attrition products of various rocks — daij in a 

 mining but not in a mineralogical sense. This clay is usually on the 

 hanging wall and is called alta. 



The other mines of the district contained similar ores in similar rocks. 

 The Guadalupe was the most productive, but was not at work and was full 

 of water during my visit. 



All the deposits of the district appear to occur along a rather simple 

 fissure s3-steni. The main fissure is uearly parallel to the rhyolite dike at 

 the Guadalupe. It follows the direction of the hills, the axis of which curves 

 gradualh' away from the dike for a certain distance. Passing through or 

 near the San Antonio and Enriquita, it seems to break across the ridge at 

 the America and enters the Almaden on the strike of its two great fissures. 

 It is near this fissure that new ore bodies are most likel}' to be found. The 

 Washington seems to be on a branch of the main fissure. 



This fissure was probabl}- formed at the time of the rhyolite eruption, 

 to which also I ascribe the genesis of tlie ore. 



Steamboat Springs. — This curious thermal area lies just within the desert 

 Great Basin, in full sight of the forests and snows of the Sierra Nevada. 

 It is onlv six miles in a straig-ht line from tlie Comstock lode. 



Granite underlies the district and much of the area exposed is of this 

 rock. Upon it lie metamorphosed rocks of the Jura-Trias series and lavas. 

 Older andesites and younger asperites, described in a former paragraph, 

 cover a large space, and there is a considerable area of basalt, which repre- 

 sents the last eruption. 



The springs are numerous and some of them reach the boiling-point. 

 They are unquestionably of volcanic origin and due to the basalt eruption. 

 They reach the surface in the granite area. The flowing springs are con- 

 fined at ))rescnt to a small group of fissures, but steam in small quantities 

 issues at many points in the region marked by evidences of solfataric action, 

 and this region is substantially a continuous one. In some portions of it 

 the sinters are cbalcedonv, in others they consist to a considerable extent 



