136 
POPULAR SCIENCE REVIEW. 
arrangements were described by the author in the 4 Journal of 
the Society of Arts,’ 1875. 
Granite, as is generally known, consists mainly of three dis- 
tinct minerals, quartz, felspar, and mica. In the decomposed 
granite it is the felspar only which is decomposed, or converted 
into kaolin ; but this renders the whole mass so soft that a pick 
or shovel may be readily driven into it to a considerable depth. 
The mode of working is to break up a portion with a pick to 
a depth of several feet, in a kind of slope, around the mouth 
of the pipe or launder which passes down into the adit below. 
This is called a 44 stope.” A stream of water is then made to 
flow over the broken lumps, which are kept well stirred up by a 
workman, called a 64 washer,” whose duty it is to keep breaking 
and stirring them up. The water, clear at first, speedily 
becomes white and milky by washing out the soft decomposed 
felspar, and runs down to the bottom of the stope, carrying with 
it the quartz grains and flakes of mica. The quartz and the 
coarser mica flakes, called 44 sand ” by the workmen, settle in a 
shallow pit, called the sandpit, from whence they are constantly 
shovelled out by a man placed there for that purpose — while 
the stream of clay water, carrying with it many minute flakes 
of white mica, passes on down the vertical launder and through 
the adit-level to be further treated. 
The stream of clay water, if thick, contains usually about 2 
per cent, of clay, and perhaps one-half per cent, of mica in 
suspension. This is made to flow slowly through a succession of 
narrow channels, called 44 drags ” and 44 micas,” in which the fine 
mica and a little clay are gradually deposited, while the bulk of 
the clay passes on with the water, and falls into a circular pit 
from twenty to thirty feet in diameter, and eight or ten feet 
deep, lined usually with granite blocks. Here it gradually 
settles to the bottom, while the clear water passes off at a 
little depression in the rim of the pit, and may either be 
pumped up to be used over again, or allowed to flow into the 
nearest river. This effluent water is often clear enough to 
drink.* 
Once or twice a day it becomes necessary to clean out the 
long channels, called 44 drags ” and 44 micas,” in which case the 
fine mica and clay, which has settled at the bottom, is washed 
out into the nearest watercourse by a stream of water, and this 
it is which fouls the streams. 
In some works, as at the celebrated Carclaze Mine, worked 
• Occasionally these pits are left filled with clay water, and undisturbed 
for several weeks, when the intense blueness of the water equals that of some 
Alpine lakes, and is due to the same cause — the suspension of minute parti- 
cles of solid matter. 
