B. Silliman on the Grass Valley District. 239 
ble evidences of an aqueous origin are seen in Massachusetts 
Hill, Ophir Hill, Allison Ranch, Kate Hayes and Eureka. 
The metallic contents of Grass Valley veins vary extremely, 
some carry but very little or no visible gold or sulphurets, al- 
though the amount of gold is found in working in mill to be satis- 
factory, and the sulphurets appear on concentrating the sands 
mcrushing. This is the case in the Lucky and Cambridge 
mines, for example. But in most cases, the veins of this dis- 
trict abound in sulphurets, chiefly of iron, copper and lead, the 
eases contents varying greatly in the same vein; zine 
and arsenic are found also, but more rarely. The most noted 
example of arsenical sulphurets are in the Norambagua an 
on Heuston Hill; lead abounds in the Union Hill lodes (as 
galena,) and the same metal is found associated with the yellow 
Copper in parts of the Eureka mine. The gold when visible is 
