Geological researches in China, Mongolia, and Japan, during the years 1862-1865.

92 GEOLOGICAL RESEARCHES IN
<'?' Q,' *',,5, a w Fig. 13 _I{''?;~~!{I'~~~............... —
The ~_ bed~_~ o vsFig. 14
a. Reservoir. b. Sluice-ditch. c. Rubble of the drift. d. Aurif. drift. e. Creek. f. Bedrock. g. Mats.
At the place where I saw this process, the surface of the bed rock, in this case
the marine terrace deposit, was sufficiently high above the creek to give a rapid fall
in the sluice-ditch.
The bed of a rivulet is chosen for the work. A reservoir (a) is dug and
dammed, and the bed of the rivulet (b) cleaned out and made regular. This done,
the banks (d) are broken down into the stream where the force of the current concentrates the gravel, carrying off the sand and clay. The workmen then place
themselves in pairs up and down the stream near and below the broken-down bank.
Each man is provided with a coarse mat, about two feet long by one foot broad,
which he places lengthwise in the stream, keeping it down with one foot on the
lower end, at the same time partially stemming the current. He then hoes the
gravel on to the mat, much of the old gravel going off below as fresh arrives from
up stream.
At intervals the mat is carefully removed and washed out into a very shallow tray
or batea (Fig. 15), a board about eighteen inches long by a foot broad, hollowed out,
and having a circular depression near one end for the concentrated head. Of the
black sand obtained on this board, the head containMig. 15 ing the gold is saved.
In this manner the gravel is pretty well exhausted
of its gold, very little being obtained by the men
A =_ Z 3 farthest down the stream. The working progresses
sideways, into the banks, and up stream, the current
being kept near the banks as these recede from the
centre of the stream. As the space between the
banks widens, the coarser material that resists the
force of the Water is thrown up into a pile of loose
masonry (c) which increases in length and breadth as the work advances.