HEAT PHENOMENA. 233 



ture. There are many miles of drifts on the Comstock flooded to a greater 

 or less extent; but a great number of observations made by my party show 

 that the water is liottest when it issues from the rock, and cools off by 

 standing in the workings. When the water at its entrance is tepid or cool, 

 it appears to remain so indefinitely, even though it may be stagnant 



Examination of the theory of kaoiinization. — Wliilc no fact Can bc better establi.shcd 

 than that the solidification of water liberates heat, no direct conclusions can 

 be drawn from it as to the relations of the complex process of kaoiinization. 

 The constitution of the unisilicates is still very obscure, and there is no 

 unanimity of opinion among mineralogical chemists, even as to the formu- 

 las by which they should be represented, while almost nothing is known of 

 the reactions which go on during decomposition. It may not be amiss, 

 however, to examine the question from a theoretical point of view. 



Feldspar assumed as representative. As liaS beCU sllOWn iu Chapter III., the fcld" 



spars of the diorite and diabase which form the walls of the Comstock are 

 apparently labradorite and oligoclase Whether Professor Tschermak's 

 theory of the feldspar group is correct or not, a mixture of these feldspars 

 may for the present purpose be regarded as a compound of one molecule of 

 anorthite and one of albite. The mixed or intermediate (andesine) feldspar 

 may then be written 



_. ,. . CaAl ) 



Na Al ■) f 



lAn + lAb = (CaAl)Si20^ + „., Si^O^-'^Na^AiySi^O^l 



Si" y „., \ 



or J 

 First step of decomposition. — The examiuatiou of thin sections leads me to be- 

 lieve that the first change in the feldspars of the Washoe rocks is the 

 formation of calcite, accompanied by a separation of silica. The formation 

 of sodium silicate probably takes place at the same time, but is not traceable 

 by optical means, for it will dissolve, and either pass out of the rock or 

 become diffused through it. If from the above formula 



CaO + SiO' and Na'^'SiO' 

 ai*e subtracted, it becomes 



Al \ 



Al > Si^O'^ 



Si^ ) 



