[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-décrit est effectivement une émanation du gypse, et non pas une matière hétérogène amenée d'autre part et déposée, 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 progénéré de chaux, détaché de son lieu natal, et exposé aux changemens de saisons, s'amollit, reçoit de crevasses, perd sa transparence, devient, enfin, tout-à-fait opaque, le phlogistique s'en évapore, l'acide en est détaché, lavé, et de terre vitrescible, qu'il étoit, il redevient chaux, comme il étoit auparavant."