54 Mr H. M. Stoker on the China-stone 
ders, where the clay, being lighter than it, leaves it deposited 
in these inclined pits, which are generally three or four in 
number, placed in tiers, with a slight elevation at the upper 
end of each. They vary in length from 10 to 20 feet, are 
generally 3 feet in breadth, and 6 or 9 inches deep, though 
both the number, size, and degree of inclination vary with 
the size and rapidity of flow of the shear of water, though no 
less than with the amount of mica contained in the stope. In 
some clay works the shear is so large that most of the mica 
is carried on with the clay, so that it possesses, when fused, 
a greater degree of tenacity, though of an inferior quality as 
to whiteness, plasticity, &c. In the separation of the best 
clays, these pits require that the motion of the shear through 
_ them should be slow and equable; the shear of small size, 
and the launders should be tapped or cleared out once in 
every Six or seven hours; a careful attention to which well 
repays any amount of labour in the production of a good ar- 
ticle. That portion of the mica collected in the first of 
these launders often being mixed with scales and crystals 
of hornblende, or diallage, is thrown aside as useless, while 
that collected in the others is generally sold as a second quality 
clay. 
The clay water, having left the mica, now flows on to a 
large circular or oval collecting pit, 30 or 40 feet in circum- 
ference, and from 6 to 10 feet deep, where the clay subsides, 
forming an under-stratum of the consistence of cream, the 
supernatant water flowing off from the top of the pit, until it 
is filled. As soon as this happens, the clay is allowed to pass 
out by a trap-hatch to the pans below it; or, should there be 
none at this level, recourse is had to the pumps, by means of 
which, and attached launders, the clay is passed to the dry- 
ing-pans in any portion of the work. Of these there should 
be from ten to twelve capable of holding from 40 to 50 tons, 
to each large collecting pit ; they have been made, till lately, 
on any part of the adjacent ground, frequently on that co- 
vering the clay bed, where the surface, after being levelled 
and covered with fine loose gravel, is hedged in by walls of 
granite, the joints of which, as well as those of the pits, 
are rendered impervious by interposed moss; they are gene- 
