and the recently discovered Porcelain-Clay. S59 
tion to repeat the analysis on the clay in its native state. The 
clay is known in commerce by the name of Cambria. 
It forms a thick bed, the extent and exact depth of which 
has not been ascertained. It is found in several adjacent mines. 
In a shaft one mile west of the present clay-pit, it occurs twenty 
yards below the surface ; as also in another mine a quarter of a 
mile south of the pit ; and it may possibly be discovered in 
other parts of this district. No attempt has been made, by 
boring through the bed, to ascertain the depth of this clay ; 
but Mr Bishop having sunk a shaft about twenty-six yards 
E. SE. of the deepest part of the pit, found different layers of 
coloured clay, and also this pure white clay, almost to the depth 
of sixty yards from the surface. At this depth, the workmen 
came to limestone. From this shaft, in which there are indica^ 
tions of lead-ore, a level is driving for draining the pit, by bring- 
ing its waters in contact with the rock, which is full of rents, 
and has sufficient fall for this purpose. When this operation is 
completed, we shall ascertain the depth of the white clay, which 
appears to constitute a very thick unequal bed. The clay ap- 
pears to be purer the deeper it has been yet explored. In 
some places it is contaminated by nests of bright yellow clays ; 
but the great mass of it is pui^e white. Among the white sand, 
and also in the clay, is found a greyish-white crumbling stone, 
with a slaty structure, which seems a transition of siliceous-slate 
into this clay ; holding the same relation to them that shale does 
to common clay and clay-slate. From its appearance, it might 
be supposed a siliceous slate, heated to redness, and then plunged 
into water. Its constituent parts are the same as the ingredients 
of the clay ; and it is now in great request with the potters, un- 
der the name of Roch Cambria. The occurrence of this sub- 
stance with the sand and clay, would lead us to consider the 
two latter either as arising from the decomposition of siliceous 
slate, or as the materials of that rock arrested, by some unknown 
cause, in their consolidation, ere the cohesion of their particles 
had united them into a homogeneous mass. It is shipped for 
. 12s. 6d. per ton, and is now employed in the potteries as an ex- 
cellent substitute for Gravesend flints. 
The clay is dug out of an open pit; and, after being diffused 
