THE WASHOE ROCKS. 119 



on which work by my parties has already begun, and to 

 which my whole attention will be given for many years to 

 come. It is not unreasonable to expect, that in the exten- 

 sive area which will there be examined, some 12,000 square 

 miles, the questions raised at Washoe will be presented, in 

 a sulficient varietv of forms, to ensure correct solutions. 



Condusiom. — While I do not deny that the granular and 

 granitoid rocks are simply those which have cooled at great 

 depths and under great pressure, I can see no evidence at 

 Washoe to prove it. Pressure and depth, not improbably, 

 tend to produce the effects which Messrs. Hague and 

 Iddings ascribe to them, but I am certain that in many 

 cases, minute differences of chemical composition produce 

 effects greater than differences of depth of, say, from one or 

 two thousand feet. ^*^ 



The only important changes which I feel called upon to 

 make in the results of my former investigation of the Com- 

 stock lode are that hypersthene is present in the pyroxenic 

 rocks, and that the area of these rocks laid down on my 



Note i^. — An eruptive magma is probably never fluid enough to become thor- 

 oughly homogeneous, and where the products of the chemical reactions are 

 multifarious, it is to be expected a priori that minute differences in composi-' 

 tion should estciblish strong tendencies which may manifest themselves either 

 in the mineralogical or the structural results. Observation also shows that 

 cases are very frequent in which adjoining rock masses so related that 

 they cannot have been subjected to different physical conditions, exhibit dif- 

 ferences not otherwise to be accounted for. Easy as it is to ascertain the 

 ultimate composition of rocks, every one recognizes that we know too little 

 as yet of the intricacies of mineral chemistry to be able to establish a 

 thorough correlation between the composition and the lithological results. 

 One road to a more satisfactory knowledge of this subject appears to be pre- 

 sented by the principles of thermo-chemistry. I have attempted a slight 

 theoretical advance in this direction in an article which will soon be printed. 

 [American Journal of Science, vol. .31, 18S6, p. 120]. Meantime, although it 

 as yet impossible usefully to employ quantitative determinations so accurate 

 as those which chemists are in the habit of making, it is most desirable that 

 these records should be correctly kept. I pointed out in my memoir on the 

 Comstock, that two analyses, originally published in the reports of the Ex- 

 ploration of the 40th Parallel, contained inconsistent data. These analyses 

 are numbered V, and VII, by Messrs. Hague and Iddings (page 33), who 



