242 B. Silliman on the Grass Valley District. 
deepest mines, for example, Hayward’s Eure a, in Amador, 
1,200 feet, North Star, 750 feet on the slope, Princeton, in Mari- 
of good ore, became suddenly poor, at a depth of over six 
hundred feet, in 1865; but I'am informed by Mr. Hall, the 
present superintendent, that the good ore came in again ina 
short distance. Mr. Laur, the French engineer, whose pa 
experience of every gold mining district offers examples in illus- 
Sloat of these remarks, In quartz veins containing a consider 
sh we of sulphurets, it is evident that the outcropping 
should yn much better returns to mining industry than W 
use above this line nature has set free the gold for- 
times that th €s of treatment, with the added advantage 
: mes, tan ho particles of free gold formerly distributed through 
» considerable section of the yein, are found concentrated in 
such amount of ore. It is eas to reach the conclusion 7 
n cases, that the amount of gold in the vein is less in depth, 
