PEEVIODS INVESTIGATFOlSrS. 19 



the CoMSTOCK vein, we may take it for granted that it caused the rending of 

 the fissure. 



Applicability of the ascension-theory. — We liavc iu the clemcnts evolved during 

 the first two periods of solfataras, namely, fluon'ne, chlorine, and sulphur, 

 all the conditions required for filling the Comstock fissure with such sub- 

 stances as those of which the vein is composed. Steam, ascending with 

 vapors of fluosilicic acid, created in its upper parts (by diminution of pressure 

 and temperature, according to well-known chemical agencies) silica and sili- 

 cofluohydric acid, the former in solid form, the latter as a volatile gas, which 

 acts most powerfully in decomposing the rocks it meets on its course. The 

 chloride of silicon in combination with steam forms silica and chlorhydric 

 acid. Fluorine and chlorine are the most powerful volatilizers known, and 

 form volatile combinations with almost every substance. Besides silicon, 

 the metals have a great affinity with them. All those which occur in the 

 CoMSTOCK vein could ascend in a gaseous state in combination with one or 

 the other of them. They must then be precipitated in the upper parts as 

 metallic oxides or chlorides, and in the native state. Thus the fissure was 

 gradually filled from its upper portion downwards, vvith all the elements 

 which we find chemically deposited in it. A fissure is ordinarily not sta- 

 tionary after its first opening; but by subsequent action may from time to 

 time widen and frequently contract again. New channels would thus be 

 opened where the old ones were obstructed. If such widening or opening of 

 an empty space within the matter filling the old fissure was followed by 

 emanations licli in metallic vapors, then the conditions would be given for 

 the formation of a body of ore of the shape of the newly-opened chasm, 

 which corresponds precisely to most of the bodies of ore in the Comstock 

 Lode. Contemporaneously with the filling of the fissure, the adjoining rock 

 would be acted upon by the ascending acid vapors, and its nature by them 

 entirely changed. Cracks would form in it, and be filled with substances 

 similar to those of the vein itself As the Comstock vein has an eastern 

 dip, and the action of forces manifests itself towards the surface, only the 

 rock on the hanging wall, or the eastern country, would be influenced in 

 this way. Crevices branching off from the main fissure would probably pen- 

 etrate into the hanging wall, and it may reasonably be expected that deeper 



