hich is very common or general on those
occasions; this is the parts or particles of stone floating in the fluid
siliceous substance, and there dissolving more or less.

M. de Carosi describes very systematically the generation of silex,
calcedony, onyx, and quartz, in calcareous earth, marl, gypsum,
sand-stone, and also what he terms _terre glaise, ou de l'Argile_. It is
in this last that we find a perfect analogy with what is so frequent in
this country of Scotland. These are the agates, calcedonies, calcareous
and zeolite nodules, which are found produced in our whin-stone
or subterraneous lavas, that is, the amygdaloides of Crondstedt.
Naturalists explain the formation of those nodular bodies differently.
The Chevalier de Dolomieu supposes these rocks to have been erupted
lavas, originally containing cavities; and that these cavities in the
solid rock had been afterwards filled and crystallised, by means of
infiltration, with the different substances which are found variously
concreted and crystallised within the solid rocks. Our author, on the
contrary, supposes these formed by a species of chemical transmutation
of calcareous and argillaceous earths, which, if not altogether
incomprehensible, is at least not in any degree, so far as I know, a
thing to be understood.

This is not the place where that subject of these particular rocks,
which is extremely interesting, is to be examined. We shall afterwards
have occasion to treat of that matter at large. It is sufficient here to
observe, that our author finds occasion to generalise the formation of
those petrifactions with the flintifications in calcareous and gypseous
bodies. When, therefore, the formation of any of them shall be
demonstrated, as having taken its origin in the fusion of those
substances, this mode of operation, which is generalised in the
consolidation of strata, will be properly inferred in all the rest.

Petrifaction is a subject in which mineralogists have perhaps wandered
more widely from the truth than in any other part of natural history;
and the reason is plain. The mineral operations of nature lie in a part
of the globe which is necessarily inaccessible to man, and where the
powers of nature act under very different conditions from those which we
find take place in the only situation where we can live. Naturalists,
therefore, finding in stalactical incrustation a cause for the formation
of stone, in many respects analogous to what is found