In granite these cavities are commonly lined with the crystal corresponding to the constituent substances of the stone, viz. quartz, feld-spar, and mica or talk.  M. de Saussure, (Voyages dans les Alpes, tom. ii. sec. 722.), says, “On trouve frequemment des amas considerables de spath calcaire, crystallise dans les grottes ou se forme le crystal de roche; quoique ces grottes soient renfermees dans le coeur des montagnes d’un granit vif, & qu’on ne voie aucun roc calcaire au dessus de ces montagnes.”

So accurate an observer, and so complete a naturalist, must have observed how the extraneous substance had been introduced into this cavity, had they not been formed together the cavity and the calcareous crystals.  That M. de Saussure perceived no means for that introduction, will appear from what immediately follows in that paragraph.  “Ces rocs auroient-ils ete detruits, ou bien ce spath n’est il que le produit d’une secretion des parties calcaires que l’on fait etres dispersees entre les divers elemens du granit?”

Had M. de Saussure allowed himself to suppose all those substances in fusion, of which there cannot be a doubt, he would soon have resolved both this difficulty, and also that of finding molybdena crystallized along with feld-spar, in a cavity of this kind. sec. 718.

To this argument, taken from the close cavities in our agates, I am now to add another demonstration.  It is the case of the calcedony agate, containing a body of calcareous spar; here it is to be shown, that, while the calcareous body was altogether inclosed within the calcedony nodular body, these two substances had been perfectly soft, and had mutually affected each others shape, in concreting from a fluid state.  In order to see this, we are to consider that both those substances have specific shapes in which they concrete from the third state; the sparry structure of the one is well known; the spherical or mammelated crystallization of the calcedony, is no less conspicuous; this last is, in the present case, spherical figures, which are some of them hemispheres, or even more.  The figures which we have now in contemplation are so distinctly different as cannot be mistaken; the one is a rhombic figure bounded by planes; the other is a most perfect spherical form; and both these are specific figures, belonging respectively to the crystallization of those two substances.

The argument now to be employed for proving that those two bodies had concreted from the fluid state of fusion, and not from any manner of solution, is this:  That, were the one of those bodies to be found impressing the other with its specific figure, we must conclude that the impressing body had concreted or crystallized while the impressed body was in a soft or fluid state; and that, if they are both found mutually impressing and impressed by each other, they must have both been in the fluid and concreting state together.  Now the fact is, that the calcareous body is perfectly