30 LeConte and Bising— Metalliferous Yein-fm 



in a different stratum ; 

 barren rock between ; 

 and appearing in the shattered sandstone on one side or the 

 other. In some places it is extremely rich— a mere breccia 

 with cinnabar paste— often the cinnabar constituting more 

 than one-half the weight of the whole. No free sulphur was 

 found at this depth nor in the wagon-spring cut; nor indeed at 

 any depth greater than a few yards below the surface. 



The origin of the brecciated layer is an interesting question. 

 During our last visit we found, outcropping in several places 

 near the lake margin, farther to the Southwest, beyond the 

 limits of the solfataric action and striking in the direction of 

 the Bank, an ordinary brecciated stratum consisting of angular 

 fragments of sandstone and shale united by a stony paste. 

 This is probably the same as the rubble-mud stratum of the 

 Wagon spring cut, only in this case the stony paste has not 

 been reduced to mud by solfataric action. It is also probably 

 the same as, or similar to, the brecciated ore-bearing stratum of 

 the underground works, only in this case the paste has not been 

 replaced by deposits from the solfataric waters. This therefore 

 seems to represent the original condition of the ore-bearing stra- 

 tum. It seems probable therefore that there was here a brecciated 

 stratum (or perhaps several sucb th the other 



strata of sandstone and shales and tilted along with these in 

 the process of mountain formation; and that being a plane of 

 weakness, this stratum was loosened and shattered by repeated 

 subsequent back-and-forth crust movements connected with 

 the volcanic eruptions, and thus became a way for ascending 

 waters. But the extreme irregularity of the ore- 

 bearing fissures shows that the loosening and shattering was 

 not wholly confined to the brecciated layer, but especially 

 where the inclination of the strata was not very high, passed 

 from stratum to stratum, following now one now another in an 

 uncertain way. Thtoi red rock, whether in 



the original brecciated layer, or in the sandstones and shales on 

 either side, the solfataric waters came up and deposited and is 

 still depositing its freight of silica and metallic -ailphides. 



Krp/auation of the phenomena. — The ridge of lava which ter- 

 minates in Sulphur Bank may be a stream from one of the 

 nearest volcanos, to which it can be almost continuously 

 traced ; or it may be the remains of a very viscous eruption 

 coming up through a fissure and spreading but little; and thus 

 g a lava stream. We have assumed the former as by 

 far the more probable, because it can be traced almost continu- 

 ously to a neighboring crater, the rock of which is identical 

 with that of Sulphur Bank, but the question can be definitely 

 settled only by continuing the tunnels beneath the lava cap 



