THE WASHOE ROCKS. 109 



pings and that at the 3,000 foot level. The distance between 

 these exposures is about 4,200 feet. Since the pressure must 

 have differed more for these two points than for points 

 equally removed on a horizontal line at the inner end of the 

 tunnel, and since the difference of distance from the original 

 surface of these points on the dip Ccin hardly have been less 

 than that for corresponding points on the tunnel, a much 

 greater difference in degree of crystallization would be ex- 

 pected on the dip of the lode than in an equal distance on 

 the tunnel. Similar remarks apply to the diabase. The 

 variation of the rate of increase of crystallization indicated 

 by Messrs. Hague and Iddings is the reverse of that of the 

 rate of cooling, while theory and experiment seem to indi- 

 cate that these two quantities sliould vary in the same 

 sense. The grains which Mr. Iddings measured are largely 

 those of secondary quartz and perhaps other secondary min- 

 erals. These secondary crystals appear actually to increase 

 as the lode is approached, as would be expected. The Su- 

 tro Tunnel and, so far as is known, the Washoe district af- 

 ford no valid proof of progressive increase of crystallization 

 in holocrystalline rocks. 



OTHER DISPUTED POINTS. 



JJiorites. — xllthough the main issues have now been 

 treated, it appears unavoidable to make some remarks as to 

 other points upon which Messrs. Hague and Iddings dis- 

 agree with me. I have already mentioned in this paper the 

 relations between the porphyritic diorites and the granular 

 forms of the same rock which make it impossible to sepa- 

 rate them. I also enlarged upon the same relation in my 

 memoir on the Comstock. The area I have laid down as 

 diorite is, I repeat, after re-examination, substantially one 

 rock. If (as my opponents claim) the porphyritic diorite is 

 hornblende andesite, then the whole mass of Mount David- 

 son is hornblende andesite and neither augite andesite, as 

 they assert, nor diorite as I believe. I am not so rash as to 



9— Bull. Cal. Acad. Sci. II. 6. Issued November 6, 1886. 



