and the recently discoverea PorcelahuClay, 
No. 3, 
Cambria Mixture. 
1| Cambria. 
4 Blue Clay. 
1 Rock Cambria. 
No. 4. 
Common Mixture. 
4 parts Blue Clay. 
I Cornish Clay. 
1 Flint, 
The proportions in the two last mixtures are said to produce 
a great improvement in the appearance of the ware ; and though 
the Cambria mixture No. S. still maintains its superiority., it costs 
less than the common mixture No. 4. 
The fine Halkin clay has also been used in the manufacture 
of the finer sorts of porcelain, for which it seems well adapted, 
by its purity and whiteness. The proportions in which it en- 
ters into porcelain, I am unable to state, because each manufac- 
turer keeps the relative proportions of the constituents of his 
china a profound secret. There can be little doubt, that the 
employment of this substance will improve the appearance of 
our porcelain ; and, when its qualities are sufficiently investi- 
gated, it promises to diminish the cost of production ; for the 
particles of the clay, already reduced almost to an impalpable 
powder, will require but ffittle further comminution, to ^render it 
immediately applicable to the purposes of art. 
There may be some difficulty in designating this clay, ac- 
cording to a received mineralogical nomenclature. Notwith- 
standing the great difference in the proportion of its ingredients 
and those of the porcelain-clay of our systems, it should, I think, 
be considered merely as a variety of this substance, which can 
only be reckoned a mechanical mixture, and therefore may ad- 
mit of considerable differences in the proportion of its consti- 
tuents. 
The discovery of this clay and of the buhrstone, induced me, 
when iately in that vicinity, to revisit Halkin ; and I submit 
this sketch, the result of a short examination of the mountain, 
— ^trusting that the imperfections of the paper may find some 
palliation, in my desire to diffuse the knowledge of discoveries 
so important to my countrymen. 
Liverpool, ) 
mil Dec. imO. j 
