294 



Mr. J. A. Phillips on the Chemical [Mar. 12^ 



sion to regard the eclipse-observations as a principal subject of attention, 

 I shall hav^e no excuse for not prosecuting preliminary arrangements, and 

 for not forwarding fuller information of my success or otherwise. 



" I am. Sir, yours very truly, 



J. Herschel." 



March 13, 1868. 



Dr. WILLIAM ALLEN MILLER, Treasurer and Vice-President, 



in the Chair. 



The following communications were read : — 

 I. Notes on the Chemical Geology of the Gold-fields of 

 California." By J. Arthur Phillips. Communicated by 

 Prof. A. C. Eamsay. Received February 22, 1868. 

 (Abstract.) 



Rocks of the Gold-Regions of California. — The great sedimentary me- 

 tallic belt of California lies on the western slope of the Sierra Nevada, be- 

 ginning in the neighbourhood of the Tejou Pass, and extending through 

 the state to its northern limit. In consequence, however, of various local 

 circumstances, different portions of this band are of very miequal impor- 

 tance as gold-producing districts. 



The slates of the auriferous belt have been shown by Professor Whitney 

 to belong, for a great extent, to the Jurassic period, although the occur- 

 rence of numerous Triassic fossils in the gold-bearing rocks of Plumas 

 County and elsewhere renders it more than probable that no inconsider- 

 able portion of the slates in the heart of the gold region are of that age. 



The rock constituting the principal mass of the Sierra Nevada is a 

 granite containing only a small proportion of quartz, and in which but one 

 species of felspar (oligoclase) is generally found. 



Lying between the band of metamorphic slates and the great central 

 mass of granite forming the more elevated portions of the chain, are 

 found various crystalline rocks, such as syenites, diorites, and porphyries. 



Quartz Veins. — The matrix or gangue of the auriferous veins of Cali- 

 fornia is invariably quartz, which is generally crystalline in its structure, 

 or partially vitreous and semitransparent. In the majority of cases the 

 quartz constituting an auriferous veinstone is ribboned in such a way as 

 to form a succession of layers parallel with the walls of the lode itself ; and 

 some one or more of these laminae are not unfrequentiy far more produc- 

 tive than all the others. In some instances these parallel bands are sepa- 

 rated from each other by a thin layer of quartz, slightly differing, either in 

 colour or structure, from that forming the seams themselves ; or they may 

 be only distinguished by a difference of colour of two adjoining members 

 of the series. 



