Par-fois il y a aussi du spath calcaire
crystallise, mais cela est extremement rare. Quelque-fois enfin ces
cavites sont remplies d'une noix de calcedoine. Je n'ai reussi qu'une
seule fois en cassant un pareil silex en boule d'y trouver encore le
reste de l'eau de crystallisation."
The only remark that I would here make is this, that, if the
crystallization of those close cavities in the _silex_ had at any time
required water of solution, it must always have required it. But, if
there had been water of solution contained in those close cavities, for
the crystallization of the various things which are often found within
them, How comes it that this water is almost never found? I have good
reason to believe that water contained within a solid flint will not
make its escape, as does that contained in the _anhydrites_ of Mount
_Berico_, which are composed of a porous calcedony. But the siliceous
crystallizations within close cavities is a curious subject, which we
shall have occasion to examine more particularly in treating of agates.
We now proceed to the next section, which is the generation of silex and
quartz in marl, (p.
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