388 GEOLOGY OF TOE COMSTOCK LODE. 



lire. It is a serious question liow far down it will be jjossible to push the 

 mines in spite of the terrific heat. 



The origin of the high temperature of the Comstock has been sought 

 in the kaolinization of the feldspar contained in the country rock and in 

 residual volcanic activity.' 



Kaolinization hypothesis. — Tlic tlicory that kaoliuizatiou is the cause of the 

 heat appears to rest upon two positive grounds — that tlie solidification 

 of water liberates heat, and that flooded drifts have been observed to grow 

 hotter. It is also claimed in favor of the kaolinization hypothesis by its 

 author that there is no evidence of any other chemical action proceeding 

 with sufficient activity to afford an expLanatlon, and that the retention of 

 igneous heat in the rocks is a sheer impossibility, while the hypothesis that 

 the heat is conveyed from some deep-seated source to the mines by means 

 of currents of heated water is characterized as somewhat violent and as 

 unnecessary. 



So far as I am aware, there are no theoretical grounds upon which 

 the heat involved in kaolinization can be estimated. The decomposi- 

 tion of feldspar into kaolin and other products (supposing kaolin to result 

 from the decomposition of plagioclase) involves several processes, of 

 which some are more likely to absorb than to liberate heat. But sup- 

 posing an anhydrous aluminium silicate formed without loss of heat, the 

 thermal results of its combination with water are by no means certain. 

 Were the water contained in kaolin not water of hydration, but chemically 

 combined, it would be possible from known experiments to compute approxi- 

 mately the heat which would be produced. It is shown in Chapter VII. 

 that the corresponding temperature would be so high as to be utterly at 

 variance with known facts. The water is therefore the water of hydration. 

 Of the heat involved in the hydration of salts we know that it is usualh' 

 small, that it is sometimes negative, and that the different molecules of water 

 combine with differing amounts of energy, but of the heat of hydration of 

 kaolin we know nothing. 



With a view to testing the theory of kaolinization as far as possible, 

 Dr. Barus, at my request, undertook some very delicate experiments 



• Frictiou ;iu(l tlic oxichiliuu of pyrite liavo also been suggested, but have iiot been serionsly advo- 

 cated. 



