436 THE CANADIAN NATURALIST. [Vol. ix 



•tudies of John Arthur Phillips, ^ho has shown that a great part 

 of the silicious deposit from certain thermal waters of Lake 

 County, California, and from the Steamboat Springs of Washoe 

 County, Nevada, is of the nature of crystalline quartz. 



[Mr. Phillips has, since the first printing of this note, in- 

 formed the writer in a private note, of the existence of beautiful 

 crystals of quartz which had grown in a cavity found at the 

 meeting of small fissures in the auriferous blue gravel, near 

 Washington, Nevada County, California.] 



Dr. Hunt then gave an account of some observations made by 

 him at the Blue Tent placer mine, in Nevada County, California, 

 in 1877, showing that the process of depositing quartz is there 

 going on in the auriferous gravel of the rejjiion, independent of 

 thermal waters, and is connected with the sub-aerial decay of the 

 silicates in the gravel, which is here made up in great part of the 

 debris of the crystalline Huronian schistaof the region, including 

 much greenstone or diorite-rock. The gravel below the drainage- 

 level is greenish or bluish in color, and contains disseminated 

 pyrites, together with trunks of trees in the condition of lignite 

 while the feldspar, and hornblende of the greenstone are undecayed. 

 Above the drainage-level, however, these silicates are more 

 or less decomposed, the greenstone-pebbles becoming earthy 

 in texture, rusty in color, and exfoliating, and the accompanying 

 pyrites oxidized. The lignite is at the same time more or less com- 

 pletely silicified, being sometimes converted into agatized masses, 

 often with drusy cavities lined with quartz-crystals, and at other 

 times only penetrated or injected with silicious matter, which has 

 filled the pores of the exogenous wood, the vegetable tissue of 

 which still remains, often incrusted with crystals of quartz. la 

 still other cases, a slow subsequent decay of the tissue, in conifer- 

 ous woodfi, has left these silicious casts in the form of bundles of 

 fibres, which have been mistaken for asbestua. The various 

 specimens from this locality illustrate perfectly the theory of 

 silicification of vegetable structures set forth by the speaker in 

 1864,* based on his own microscopic studies conjoined with those 

 of Goppert and of Dawson. The silica by which the tissues are 

 thus successively filled and replaced is, according to the speaker, 

 that which is set free in a soluble form by the decay of the sili- 



* See Can. Naturalist, New Series, vol. i, p. 56 ; also Hunt's Chem, 

 and Geol. Essays, p. 286. 



