heir crystallizing.

_Lastly_, That as this fluid state had not been the effect of solution
in a menstruum, it must have been fluidity from heat and fusion.

Let us now make one general observation and argument with regard to
the formation of those various coated, concreted, crystallized, and
configured bodies. Were the crystallization and configuration found
to proceed from a central body, and to be directed from that centre
outwards, then, without inquiring into collateral appearances, and other
proofs with regard to the natural concretion of those substances, we
might suppose that these concretions might have proceeded from that
central body gradually by accretion, and that the concreting and
crystallizing substances might have been supplied from a fluid which had
before retained the concreting substance in solution; in like manner as
the crystallizations of sugar, which are formed in the solution of
that saccharine substance, and are termed candies, are formed upon the
threads which are extended in the crystallizing vessel for that purpose.
But if, on the contrary, we are to consider those mineral bodies as
spheres of alternate coats, composed of agate, crystal, spars, etc.; and
if all those crystallizations have their _bases_ upon the uncrystallized
coat which is immediately external to it, and their _apices_ turned
inwards into the next internal solid coat, it is not possible to
conceive that a structure of this kind could have been formed in
any manner from a solution. But this last manner is the way without
exception in which those mineral bodies are found; therefore we are to
conclude, that the concretion of those bodies had proceeded immediately
from a state of fusion or simple fluidity.

In granite these cavities are commonly lined with the crystal
corresponding to the constituent substances of the stone, viz. quartz,
feld-spar, and mica or talk. M. de Saussure, (Voyages dans les Alpes,
tom. ii. sec. 722.), says, "On trouve frequemment des amas considerables
de spath calcaire, crystallise dans les grottes ou se forme le crystal de
roche; quoique ces grottes soient renfermees dans le coeur des montagnes
d'un granit vif, & qu'on ne voie aucun roc calcaire au dessus de ces
montagnes."

So accurate an observer, and so complete a naturalist, must have
observed how the extraneous substance had been introduced into this
cavity, had they not been formed together the cavity and the calcareous
crystals. That M. de