No. 275.J 
207 
bring into closer union the particles of silex in the immediate vicinity 
of each other, and which, by a continuance of the same influence would 
produce a gradual accumulation of matter of increasing density and firm- 
ness, until finally, those movements have been imparted to the whole of 
the silex contained in the beds. The accumulations commence at dif- 
ferent points, which of course con&titute different centres of attraction; 
at each of which there forms a mass of consolidated silex or of hornstone 
or chalcedony. An analogous change takes place in the porcelain pulp 
after the materials have been ground and formed into a pasty mass in 
the vats in case it is suffered to stand long without agitation; for after 
long repose it is found that concretions of silex have already formed in 
the paste, indicating the commencement of a series of changes which 
would finally aflfect the entire composition of the materials, and which, 
if sufiered to extend would spoil the whole mass for the purposes for 
which it is prepared. 
The oxides of iron and manganese are always found as«5ociated with 
these beds; they occur in two forms; first, as concretions, which have 
been formed by the same process as the silicious; and second, as colour- 
ing materials, which are uniformly diflTused through some portions of 
the deposite. 
The oxide of manganese occurs in the original rock from which the 
clay is formed, in dendritic implantations, occupying the seams between 
the lamina of feldspar. Those dendritic implantations may have been 
formed by infiltration of mineral matter from above, or separated from 
the general mass and transferred by galvanic agency to the surfaces they 
now occupy. As the granite disintegrates and decomposes, the oxides 
undergo a partial solution, and together with the silex become in pro- 
cess of time uniformly diffused through the materials composing the 
beds. Subsequently, affinity brings the particles of manganese and iron 
together in the form of globular masses, so that we have all the elements 
of the rock, the silex, iron, and manganese, alumine and silex, each, ac- 
cording to their affinities, in the form of separate independent masses, 
or in imperfect combination. To carry our views a little farther, we 
may suppose that the same beds subjected to the action of heat, when 
another series of actions would ensue, the result of which might be the 
reproduction of the original rock, or of other crystalline bodies, as the 
silicate of alumine, iron, and manganese. We have in these changes 
and transformations, beautiful illustrations of the alterations in state and 
composition which the solid materials composing these rocky strata un- 
dergo by a modification of the force of affinity. We have too, abund- 
