No. 7.] FORMATION OP QUARTZ. 435 



of north-eastern America. Inquiries which promise to throw 

 farther light ou this question are in progress, and the present 

 note to the Academy is to be considered as only preliminary to 

 a further discussion of the subject. 



IV. ON THE RECENT FORMATION OF QUARTZ AND 



ON DILICIFICATION IN CALIFORNIA.^ 



(From the American Journal of Science, Vol. xix, May, 1880.) 



At the meeting of the American Institute of Mining Engineers 

 in New York, Feb. 13, 1880, Prof. George W. Maynard exhibited 

 a remarkable specimen lately obtained by him from the mines of 

 the Gold Run Hydraulic Co. at Dutch Flat in California. It 

 consisted of a mass of milky vitreous quartz, in which a recent 

 fracture had disclosed an imbedded fragment, about half an inch 

 in diameter, of the characteristic so-called hlue gravel of the 

 region, holdino; in its paste a worn and rounded piece of gold of 

 several grains' weight. Portions of a similar blue gravel adhered 

 closely to certain parts of the mass of quartz. Remarks were 

 made on this specimen by Professors Silliman and Egleston, and 

 by Dr. T. Sterry Hunt, all of whom, after examination of it, were 

 satisfied of the correctness of the opinion expressed by Professor 

 Maycard, that the quartz had made part of a vein formed in the 

 auriferous gravel subsequent to the solidification of the latter. 



Dr. Hunt, in commenting on this occurrence, remarked that 

 it is in accordance with what we already know of the recency of 

 some of the quartz of this region, and cited the microscopic 



* This communication had been printed and revised before the 

 writer had seen Professor Joseph LeConte's paper on the Old Eiver 

 Beds of California, in iihe Mo.rch number of the American Journal of 

 Science, where (on pages 179-181) he has so well described the auri- 

 ferous gravels here referred to, and pointed out the true relations 

 between the blue gravel and the upper and altered portions of the 

 deposit. As regards the process of silicification, it is net, I think, 

 necessary to suppose the infiltration of alkaline waters from the 

 overlying volcanic rock in order to explain the solution of the silica. 

 As elsewhere pointed out by the writer, the removal of the silica in a 

 soluble form from the silicates which make up a large part of the 

 gravel itself, does not require the intervention of alkalies. 



I hope soon to continue the discussion of this problem, which ia 

 one of the most important in the whole domain of what I venture to 

 call mineral physiology. 



