42 H. W. Fairbanks — Tin Deposits in California. 



vein matter or in stringers and bunches. In the latter case it 

 is sometimes found in nearly pure condition. The average of 

 the ore milled was however only about 5 per cent of the oxide. 

 Seams of clay are generally found on or near the sides of the 

 vein, showing some movement since the deposition took place. 

 The walls are quite irregular and sometimes bunches of granite 

 are found wholly inclosed in the vein. The analysis of the 

 ore made by Genth, and quoted by both Blake and Hanks, 

 shows silicic acid 9 '82 per cent, tungstic acid *22, oxide of tin 

 76*15, oxide of copper *27, oxides of iron and manganese, lime 

 and alumina 13*54. This must have been an exceptionally 

 pure specimen and wholly free from tourmaline. 



The tin ore occurs in two forms ; the more important and 

 common variety is either massive and of a brownish color, or 

 in clear reddish brown crystals lining cavities ; the less common 

 variety is that of " wood tin," which appears uncrystallized and 

 in the form of thin layers. 



It is not known to the writer whether the ore body which 

 was being followed down finally ran out or not, but at any 

 rate it appears that it was unprofitable to work. The great 

 richness of the ore in places is one of the remarkable features 

 of this deposit when compared with most of the other known 

 occurrences of tin. Another remarkable fact is the great size 

 of the main vein as shown in Cajalco hill and its uniformity 

 and simplicity of composition. It appears that the contents of 

 the veins represent the entire replacement of the granite bor- 

 dering what were originally narrow fissures. The agent which 

 accomplished this was probably heated water carrying various 

 minerals in solution, the economically valuable one, tin, being 

 deposited only in places under exceptional conditions. 



