SUMMARY. 389 



presently to he described. The result of these experiments, in a word, 

 was that finely divided, almost fresh cast-conntry diahase, exposed to the 

 temperature of boiling water and the action of saturated aqueous vapor for 

 a week at a time, and for several weeks in succession, sliowed no rise of 

 temperature perceptible with an apparatus delicate to the iuu^) of a degree C. 



It is by no means certain that kaolinization was effected by these exper- 

 iments. The particles of rock were indeed coated with a white powdery 

 substance, but this was probably the residuum of the evaporated water. 

 It is still possible that, when kaolinization occurs, heat is liberated. It 

 is also possible that at temperatures above tlie boiling point and pi-es- 

 sures greatly exceeding 760""", feldspars are kaolinized, but it appears 

 no longer reasonable to ascribe the heating of drifts, which are at nearly 

 normal pressure, to the reaction on the rocks of water below the boiling 

 point. The scene of active and heat-producing kaolinization, if it exists at 

 all, must, therefore, be at remote depths. As was explained in a previous 

 paragraph, the present examination has not resulted in tracing any consid- 

 erable amount of kaolinization on theCoMsrocK; while, had the heat of the 

 Lode been maintained ever since its formation at the expense of the feld- 

 spars, but little undecomposed feldspar could now remain. In short, while 

 it cannot be demonstrated that the heat of the Comstock is not due to the 

 prevalence, at unknown depths and pressures, of a chemical change of un- 

 known thermal relations, I have failed to find any proof that it is due to 

 kaolinization. 



soifataric action. — Of the origiii of tlio licat of solfataras not very much is 

 known; yet, as they commonly occur either as an accompaniment of vol- 

 canic activity, or in regions characterized by the strongest evidences of past 

 volcanic activity, it is usual and seems rational to connect them as cause 

 and eff"ect, or as different effects of a conmion cause. There seems to be no 

 special opportunity on the Comstock for an elucidation of the whole theory 

 of vulcanism, but considerable grounds for connecting the heat there mani- 

 fested with that chain of phenomena. 



That soifataric action, as commonly understood, once existed on the 

 Comstock is certain. That the time at which the Lode was charged with 

 ore is not immeasurably removed from the present, seems to be demon- 



