sum 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].

[Note 41: From the description given in this treatise, and from the
drawings both of M. de Carosi and M. Macquart, I find a very valuable
inference to be made, so much the more interesting, as I have not found
any example of the like before. This arises from the intimate connection
which is here to be perceived between agate and gypsum. Now, upon this
principle, that the agate-calcedony had been formed by fusion, a truth
which, from the general testimony of minerals, I must presume, it is
plain, that those nodules of gypsum had been in the fluid state of
fusion among those marly strata, and that the gypseous bodies had been
penetrated variously with the siliceous substance of the calcedony.

The description of those siliceous penetrations of gypsum is followed by
this conclusion: "En voila assez, je crois pour faire voir que le silex
ci-decrit est effectivement une emanation du gypse, et non pas une
matiere heterogene amenee d'autre part et deposee, ou nous la voyons."
In this instance our author had convinced himself that the calcedony
concretions had not been formed, as he and other mineralists had before
supposed, by means of infiltration; he has not, however, substituted
any thing more intelligible in its stead. I do not pretend that we
understand mineral fusion; but only that such mineral fusion is a thing
demonstrable upon a thousand occasions; and that thus is to be explained
the petrification and consolidation of the porous and naturally
incoherent strata of the earth.]

There is, however, a subject in which I can more freely accuse this
author of being deceived. This naturalist says, that calcareous stones
become silex by a certain chemical operation; and that those flinty
bodies, in being exposed upon the surface of the earth, out of their
natural bed, are again, by a contrary chemical operation, changed from
flint to a calcareous substance. I will give it in his own words, (p.
56.)

"Cela dit, venons au fait. Tout silex progenere de chaux, detache de son
lieu natal, et expose aux changemens de saisons, s'amollit, recoit de
crevasses, perd sa transparence, devient, enfin, tout-a-fait opaque, le
phlogistique s'en evapore, l'acide en est detache, lave, et de
terre vitrescib