3.28 Mr. J. A. Phillips's Notes on the Chemical Geology 



ferous veins of California, I have made analyses of the veinstones 

 from several of the most productive mines, and have examined 

 under the microscope thin sections from a great number of 

 others. My experiments have, however, been chiefly confined 

 to various lodes in the vicinity of Grass Valley, in the county 

 of Nevada, with which I have had numerous opportunities of 

 making myself acquainted, and among which are comprised some 

 of the most productive veins of the country. 



In preparing thin sections for examination I have carefully 

 avoided the use of any kind of polishing, powder; and the arrange- 

 ment made use of for examining them has generally been a J- 

 objective, by Ross, with draw-tube and eyepiece magnifying 

 about 400 linear. In some cases, however, a magnifying-power 

 of above 1000 linear was employed. 



Examination of Quartz from the Kate-Hayes Vein. — Fragments 

 of quartz taken from near the surface at the Kate-Hayes vein, 

 Grass Valley, and having a specific gravity of 2*59, gave the fol- 

 lowing results : — 



Water lost at 212° F 0-26 



Water lost by subsequent ignition . 0-70 



Silica 93-32 



Alumina 2-03 



Iron 1-291 T 



Sulphur 1<45 |Iron pyrites. 



Potash 0-40 



Soda 0-21 



Lime and magnesia traces 



99-66 

 This vein is composed of parallel bands, some of which con- 

 tain small quantities of chlorite and iron pyrites. The quartz 

 of which it consists is of a greyish colour, not very distinctly 

 crystallized, has a peculiar greasy appearance, and contains cavi- 

 ties, on the surfaces of which have been deposited guttate silica 

 of a chalcedonious description. This rock contains gold in the 

 form of large scales and plates. 



When examined under the microscope with a low power, this 

 quartz presents in some places a cloudy appearance, and is found 

 to contain a few small cubical crystals of iron pyrites, together 

 with cavities filled by chalcedonious matter. Under a higher 

 power it is seen to contain fluid-cavities of about one4housandth 

 of an inch in diameter, and in which the ratio of the vacuity 

 to the cubical content of the cavity is about 1 : 10. 



This veinstone also encloses small cavities which appear to be 

 lined with clay, and in which no vacuities can be seen. It like- 

 wise contains gas-cavities and markings very similar in appear- 

 ance to the " glass-cavities " described by Mr. Sorby as occurring 



