12 B. Silliman on the Deep Placers of 
The object of this laborious exploration is obvious. The 
long tunnel becomes a sluice-way through the whole length of 
igh enough above the pavement to control the stream. The 
pavement is usually composed of blocks of wood six inches in 
thickness and as wide as the sluice, cut across the grain of the 
wood, e are placed about two inches apart at the ends 
and held in position by cleets of two inches square. In the 
interstices (‘rifles’) of two inches by four thus left, a small 
portion of quicksilver is placed, to aid in catching the gold ~ 
which finds its way into these hollow spaces. 
The vertical shaft is intended to furnish a fall of sufficient 
height to break up the harder masses of conglomerate and 
cement as the gravelly stream is precipitated, dashing from side 
to side of the shaft, and finally with great force upon its rocky 
bottom. 
The water from the canal is brought by side flumes or aque- 
ducts to the head of the mining ground, with an elevation of : 
: mu- 
nicate at the bottom with a strong prismatic box of cast iron, 
glib ind 
