108 CALIFORNIA ACADEMY OF SCIENCES. 



The present surface of the pyroxene andesite lies some 

 1,200 or 1,500 feet nearer the original surface than the sec- 

 tion of it made by the Sutro Tunnel. If a cone of the rock 

 originally existed here, it follows from the above that the 

 surface should afford a sensibly better opportunity than the 

 Tunnel for tracing the increase of crystallization. It offers 

 the farther advantages of more extensive exposures and far 

 greater freedom from decomposition. As already pointed 

 out, however, it yields no arg anient in favor of the theory 

 propounded by Messrs. Hagae and Iddings. 



The intensity of solfataric action must approximately 

 follow the logarithmic conduction curve which, as I show- 

 ed, represents the distribution in the east country of heat 

 emanating from the lode. So far as the observation of 

 Messrs. Hague and Iddings on the ground mass of the rocks 

 refers to secondary products, it thus appears in entire con- 

 sonance with my investigations. 



Progressive crystallization not prove I at Washoe. — The case 

 with reference to progressive increase of crystallization 

 then stands as follows : On the line of the Sutro Tunnel 

 the augite andesite at the surface above the tunnel has been 

 examined for over 7,000 feet, and no tendency could be de- 

 tected to any progressive change in the rock. It is difficult 

 to imagine any conditions under which such progressive 

 tendency (if it ever existed) would not be more marked at 

 the present surface than in the Sutro Tunnel; or in other 

 words, the change between the extreme ends of the line ex- 

 amined on the surface would be expected to correspond to 

 the change on a longer line in the tunnel. Other portions of 

 the augite andesite area were examined with a similar result. 

 There is no sensible difference between the diorite at the crop- 



allowed to cool in the air, are " basaltified" or converted into a tongh, lithoid 

 mass if they are run into pits and covered with a few feet of non-condnctiug 

 material. Laboratory experiments, of course, prove much the same thing. 

 In these cases the relation of the change to the distance from the surface is 

 just what would be expected if the granulation is a simple inverse function 

 of the rate of cooling. 



