[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 vitrescible, qu’il etoit, il redevient chaux, comme il etoit auparavant.”

Here is no question with regard to mere opinion, but to matter of fact; and, in this case, nothing is more evident, than that upon the surface of this earth, that is, in the examinable parts above the level of the sea, there is no transition either of calcareous bodies into flint, nor of flinty bodies into calcareous substance.  Calcareous matter is constantly dissolved by water, when it is exposed to the washing of that fluid; and it is even dissolved out of the most perfect union or combination with siliceous substance, and the most solid composition of an insoluble body, as may be perceived in the decaying of feld-spar.  A superficial view of flints, which have come out of a body of chalk, may have created such an opinion, which will not either bear the light of chemical or mineral investigation.  The subject of these chalk flints will be minutely examined in its proper place.