503 
1877*] Cornish China Clay . 
of the county, at Blisland and St. Breward, near Bodmin, 
and in the west near Helston. Lee Moor, a part of Dart- 
moor near Plymouth, also yields considerable quantities of 
the clay ; but as the largest works there are held by mer- 
chants who are large raisers in the St. Austell district, it 
can hardly be said that the Lee Moor enterprise enters into 
any competition with the Cornish trade. 
The natural state in which the clay is found cannot be 
better described than by the following extratft from an able 
paper on “ The China Clay and China Stone of Devon and 
Cornwall,” read before the Society of Arts in May, 1876,* 
byj. H. Collins, F.G.S., a gentleman intimately connected 
with the subject 
“ In each of the granite masses which rise like islands in 
the sea of clay slate forming the western extremity of 
England, some portions have their felspar so decomposed 
as to be converted into kaolin, or china clay. Other por- 
tions are less decomposed, and of somewhat different 
composition, and these supply the china stone. These de- 
composed portions are always associated with veins of black 
tourmaline and other minerals containing fluorine. The 
mode of alteration of the granite rocks in these neighbour- 
hoods, in my opinion, has certainly been effected by fluorine 
and other substances coming up from below, and not by 
carbonic acid and water adting from above. As a rule, the 
decomposition is more general near the junctions of the 
granite with the surrounding rocks than elsewhere, but to 
this rule there are some notable exceptions. 
“ The natural clay rock is almost always covered with a 
thick layer of stones, sand, or impure and discoloured clay, 
known as ‘ overburden.’ This capping often much resembles 
glacial drift, but it never contains any scratched or glaciated 
stones or travelled blocks. This capping varies from 3 feet 
to 40 feet in thickness, and it must, of course, be removed 
before the clay can be wrought. 
“ The decomposed granite is found at all elevations except 
the very highest points of the districts, which are always 
composed of hard rocks ; but yet their situation is usually 
indicated to the practised eye by a peculiar depression of 
the surface. These depressions are not observed in the case 
of china stone. The natural clay rock, being a decomposed 
granite, consists of kaolin, irregular crystals of quartz, and 
flakes of mica, with sometimes a little schorl and undecom- 
posed felspar.” 
* A short and eminently pra&icai work, duly reported in the Society of 
Arts Journal for May 5, 1876. 
