Both M. de Carosi, and also M. Macquart[40], to whom our author
communicated his ideas and proper specimens, assert, that from their
accurate experience, they find calcedony growing daily, not only in the
solid body of gypsum, etc. while in the mine, but also in the solid
stone when taktn out of the mine, and preserved in their cabinet.
[Note 40: Vid. Essais de Mineralogie par M. Macquart.]
What answer can be made to this positive testimony of these gentlemen,
by a person who has not seen any such a thing, and who has not the
opportunity of examining the cases in which those naturalists may have
perhaps been led into some delusion? Were I however to conjecture upon a
subject in which I have not any positive information, I should suppose
that some part of the calcedony, like the _oculus mundi_ when dipped in
water, may be so transparent, while containing some portion of humidity,
that it is not easily distinguishable from the gypsum in which it is
concreted; but that in having the humidity evaporated, by being taken
out of the mine and exposed to the dry air, those portions of calcedony,
which did not before appear, may be perceived by becoming more
opaque[41].
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