THE WASHOE ROCKS. 105 



PEOGRESSIVE CRYSTALLIZATION. 



Ohservafioiis on the surface. — Messrs. Hague and Iddings, 

 however, claim to observe in my slides a progressive in- 

 crease in the coarseness of the grain of the rocks from the 

 contact between the later hornblende andesite with the 

 augite andesite to the lode itself. This is a distance of about 

 ten thousand feet. They appear to me to have been misled, 

 and for this opinion there are various grounds. Messrs. 

 Hague and Iddings admit that the later hornblende ande- 

 site is much later than the pyroxene andesite. The latter 

 has, consequently, been subject to very considerable ero- 

 sion. If, therefore, there is a progressive tendency in the 

 physical character of this rock on the Sutro Tunnel level, 

 such a tendency should also be sensible on the present sur- 

 face of this rock, lying as it must considerably below the 

 original surface, Indeed, as I shall presently show, it 

 should afford a better opportunity for establishing their 

 theory. I have gone over the entire surface area east of the 

 lode, with a view to the examination of this point. I found 

 that while the pyroxene andesite is as a whole pretty uni- 

 form, quite as much so as similar rocks usually are, it was 

 possible in any area of a few yards square to find very con- 

 siderable differences in the grain of the rock. Carrying- 

 quantities of chips about with me for comparison, I found it 

 impossible to establish anything like a tendency in the 

 crystallization. I examined with particular care a belt 

 about 7,500 feet long lying directly above the Sutro Tunnel, 

 and could detect no tendency to coarser or more uniform 

 grain at the western edge of the pyroxene andesite area 

 above the tunnel than near Shaft No. II, nor could I detect 

 anything of the kind at any intermediate point. 



Secondary Minerals in the Tunnel RocJiS. — I have also re- 

 examined the Sutro Tunnel which is no longer a satisfac- 

 tory field for observation, being now almost everywhere 

 timbered. I have carefully reviewed my own slides from 



