202 JOURNAL OF THE PLYMOUTH INSTITUTION. 
clay, with fine silica and the glistening mica, pass on. The speed 
of the water is still further reduced, and the mica, or the “shine,” 
settles out ; and finally, by passing through a set of long troughs, 
where the speed is reduced yet more, the “mica,” really the fine silica, 
settles, and only the china clay proper is allowed to flow on into 
large settling-tanks. After the clay has settled so as to leave the 
water bright and clear, the water is run off, leaving the clay with 
as little water as possible. From these tanks, when sufficiently 
settled, the clay is drawn off in a pasty condition into large drying- 
pans, constructed of fire-brick sides, and fire-clay tiles for the bottom, 
under which circulate flues from a large fireplace, leading off into a 
high chimney, whence we see little else but steam passing off. In 
this pan the clay is sufficiently dried to allow of its being cut into 
cubical masses of about 12” cube, when it is lifted out, and trans- 
ferred either direct into railway-waggons or into sheds, where it is 
kept until required for transport to place of shipment. Near the 
drying-places are large deposits of thousands of tons of the refuse 
mica and sand, of which as yet only a very limited consumptio 
has taken place. 
If we examine the ground in the stopes before it is disturbed, 
we shall find that it much resembles a rotten granite, inasmuch as 
it contains the same constituents as granite, but not in an in- 
durated condition. The ‘question has been raised, but not yet 
settled, whether we should consider it as a decomposing granite, 
or as an imperfectly formed granite which has never as yet attained 
an indurated form. I have seen rocks apparently solid and com- 
pact which on the touch crumbled to pieces, this effect having 
been produced by the exposure for an undefinable period to the 
action of hot water, which probably contained carbonic acid in 
abundance, and possibly small quantities of fluorine. May not 
these formations be attributable to similar actions? The evidence 
may be as yet incomplete for forming an opinion, but this theory 
may help investigation of accompanying phenomena. LElvans and 
metamorphic rocks may be found traversing granite ranges, and 
are they not indications of volcanic action sufficient for the supply 
of hot water? If we watch the working of the stopes we must 
notice the large quantity of dead work ; 7.e. useless material that 
has to be removed for the recovery of saleable produce. This will 
vary very much according to different localities. Thus from 10 
to 20 per cent. only may be returned ; 7.e. for every ton of market- 
