and China-clay of Cornwall. 53 
fit to be washed is placed at a depth of from 10 to 20 fathoms 
from the surface. The removal of the Superimposed earth 
is effected by a number of men with their pickaxes and sho- 
vels, which, by their barrows, they transport to the adjacent 
rugged country, so as to render it smooth and level, in order 
to form drying fields for the summer. While this is in pro- 
gress, the clay stope, over the top of which flows a small 
stream of water, is being excavated by another set of men, 
which, as the water passes through, has the clay suspended 
in it by the treading action to which the stope is subjected, 
by means of the large boots, often seven pounds weight, with 
which the clay streamers are supplied; the sand is thus se- 
parated from the clay and mica, which are carried on by the 
water, and the sand is then carried by rail or carted to the 
top of the work, whence it is taken to be spread over the 
drying grounds, or is thrown into the pits and pans. 
The water to be supplied to the clay stope should consist 
of two-thirds of spring to one-third of rain water, this mix- 
ture causing a deposit of the suspended clay much more 
readily than any other. Great attention is often necessary 
in this part of the process, as, from an excess of rain-water, 
it is often requisite that it should be saturated with some 
earthy base. Common alum is at present used for this pur- 
pose, though any other cheaper salt would answer the pur- 
pose, as it is only necessary to saturate the water fully with 
earthy bases, when the clay speedily becomes thrown down 
a law not generally known. 
As a substitute for this, I have at times had recourse to 
finely-ground peat, or wood charcoal, which, thrown over the 
surface of a pit, on which it floats, by a process of angular 
attraction or repulsion, causes the clay to be deposited, even 
from distilled water, far more readily than by the addition 
of any soluble earths, as may be demonstrated, with ease, by 
experiment in two or three tumblers; but as I am rather in 
advance of the water in which I left the clay and mica sus- 
pended at the bottom level of the clay work, I must return 
thither, till, by the aid of wooden or iron pumps, from 40 to 
80 feet deep, worked by a powerful water-wheel, this milky- 
looking fluid is elevated to the level of the large mica laun- 
