iS77*] 
Cornish China Clay . 503 
depth, the latter varying from 30 to 120 feet. Over the 
sloping sides of these workings streams of water are di- 
rected which in their course carry with them the deposit of 
clay mixed with sand and mica, the proportions varying at 
the several works, but averaging about 8 cons of sand and 
mica per ton of china clay. During the progress of the 
streams down the sides — or, as they are locally called, 
“ stopes ” — of the cuttings, shovels are used for causing the 
separation of the clay and sand, and the several streams 
meet at bottom, carrying with them the liquid mixture into 
a reservoir, where the sand and much of the mica becomes 
deposited. At some works the liquid is then pumped, and 
at others it flows from the reservoir by natural gravitation 
into a series of long channels called “ micas.” These are 
from 2 to 6 feet wide and from 4 to 9 inches deep, varying 
with requirements and size of streams to be passed, and in 
length from 100 to 500 feet. The channels have a slight 
fall, and have weirs or dams placed about 20 feet apart, 
which, of course, check the stream at intervals and cause 
the heavier portions of the mixture to fall to the bottom, 
and these latter are afterwards run off and re-washed, or 
sent away as refuse.* Passing from the “ micas,” the so- 
lution, being clay alone, flows into large “ tanks ” averaging 
about 40 feet long, 50 feet wide, and 6 feet deep, where it 
settles, the water running off as the deposit becomes denser 
and the tank fills. If the clay is to be dried in the open air 
the thickened clay is then run off from the tanks into 
“ pans,” which are excavations of from i|- to 2 feet deep, 
of various sizes, and sanded at bottom. When sufficiently 
solid the clay is cut into square blocks and ranged in rows 
on the ground, and, being exposed to the influence of sun 
and wind, soon becomes dry. Of late years, at some works, 
kilns for drying the clay have been introduced : they vary in 
length from 100 feet and upwards ; the clay is conveyed to 
them from the tanks by various methods, and their drying 
capacity differs according to circumstances and require- 
ments. 
The arrangements for transporting the clay from one part 
of the county to another are almost as complete as can be 
* A marked feature of the Cornish county, and also of parts of Devon, are 
the white and red streams of refuse water which respectively are discharged 
from the clay works, and the iron mines, and how through the green fields and 
valleys till they reach the sea, where they often form a serious obstacle to the 
prosecution of the coast fisheries. The other materials (much of which is 
used for inferior purposes, such as tiles, chimney-pots, fire-bricks, &c.) dug 
out whilst excavating china clay are overburden (common earth, rubble, &c>), 
fine mica, coarse mica, discoloured clay. 
