at Sulphur Bank, California. 31 



and ascertaining whether or not a dike is cut through. If the 

 lava cap is a stream from a neighboring volcano, as seems 

 almost certain, then its presence here has nothing to do with 

 the solfataric action or the occurrence of cinnabar. These origi- 

 nate far beneath the lava and would come to the surface, all 

 the same, if there had been no stream in this place or if it had 

 not reached so far. Eolland thinks the solfataric action pre- 

 ceded the volcanism — that the lava stream flowed over and 

 covered pre-existing solfataric vents and thus compelled the 

 waters to seek the surface through their jointed structure. 

 This may or may not be true of ream, but is 



not true of the volcanic activity of this vicinity. 

 Solfataric action usually follows rather than precedes eruptive 

 activity. We suppose therefore that with the decline of Plio- 

 cene volcanic activity of this vicinity, the solfataric action com- 

 menced, and that the solfataric waters coming up through 

 somewhat definite channels in the tilted strata, but finding 

 itself beneath the lava cap, spread in all directions thi 

 open jointed structure and so reached the surface, d< 

 more diffusely and therefore in less available form in this sur- 

 face portion. The same open joint structure has given freer 

 access to air, and therefore produced a more decided surface 

 action, as will be explained below. 



Again : There are evidently here two very different and 

 even opposite kinds of chemical action going on ; the one 

 primary and deeper seated produced by up-coming alkaline 

 subterranean waters, the other secondary and superficial, pro- 

 duced by the acid down-going surface waters. This latter is 

 greatly facilitated by the open joint structure of the lava. We 

 wish now to give a general explanation of the action of these 

 two kinds of water, and the mode of formation of the different 

 kinds of products previously mentioned. 



Action of the up-coming subterranean water. — (a.) Clay and 

 Silica. The ascending waters, by analysis, contain a large 

 amount of sulphides and carbonates of sodium and ammonium 

 with excess of carbonic and sulphydric acid. They also con- 

 tain a considerable amount of boracic acid. These waters, 

 corning up from unknown depth and at high temperature, dis- 

 solve the silica from the rocks and carry it upward on their 

 way in solution, while the rocks thus leached of their excess of 

 silica are left in the water-ways as a tough, unctuous clay — 

 colored bluish by protoxide of iron. The silica thus gathered 

 below and carried upward in solution is again deposited by 

 cooling and relief of pressure in fissures and cracks first as ge- 

 latinous silica which then gradually by loss of water becomes 

 cheesy and finally chalcedonic. 



(b.) Cinnabar. The same alkaline sulphide waters must have 



