299 
on Basalt , &c. 
would have disappeared, and the whole rock would have re- 
sembled the present basis. Hitherto, this very singular rock has 
only been found in detached fragments.* *• 
The admission that solution is not a requisite of crystalliza- 
tion, appears to me an important concession in favour of the 
aqueous system, which has laboured under very great embar- 
rassment, from the difficulty of dissolving quartz. If a very 
perfect mechanical suspension be all that is requisite, we may 
cease to wonder at the almost daily formation of petrified wood, 
(in which, though crystallization does not actually take place, 
a very perfect arrangement is indicated, by the intimate union of 
the siliceous particles,) or of hydrophanous semi-opals in the 
decomposed serpentine of Mussinet, near Turin, or of chalcedony 
containing drops of water, in the decomposed basalt of Vicenza. 
* I shall venture to quote another instance, on the authority of Professor Playfair. 
“ The salt rock in Cheshire, which lies in thick beds, interposed between strata of an 
“ argillaceous or marly stone, and is itself mixed with a considerable portion of the 
*• same earth, .exhibits a very great peculiarity in its structure. Though it forms a 
« mass extremely compact, the salt is found to be arranged in round masses, of five or 
ec six feet in diameter, not truly spherical, but each compressed by those that surround 
it, so as to have the shape of an irregular polyhedron ; these are formed of concentric 
« coats, distinguishable from each other by their colour, that is, probably, by the 
« greater or less quantity of earth, which they contain ; so that the roof of the mine, as 
“ it exhibits a horizontal section of them, is divided into polygonal figures, each with 
“ a multitude of polygons without it, having altogether no inconsiderable resemblance 
“ to a mosaic pavement. In the triangular spaces without the polygons, the salt is in 
“ coats, parallel to the sides of the polygons.” Illustration of the Hutton i an 
Theory, page 37. 
I am informed,, that the siliceous deposition at Geyser, is at first a porous friable 
mass, and that the addition of more molecules renders it fibrous ; also that, on a farther 
addition, the fibrous structure disappears, and the whole assumes the compact even 
texture of chalcedony or flint. If I am not misinformed, a series of specimens illus- 
trating this transition, existed in the cabinet of the late Dr. Hutton, of Edinburgh. 
