184 FLINT GENUS. Formation of Agate. As the explanation of the modes of formation of the different kiuds of agate, given by Werner, is in- terefting, L fhall here give a fhort datement of it. Firff, refpeding thofe kinds that occur in amygda loid : He fuppofes, that during the depofition of amvgdaloidal rocks, a confiderable quantity of aif was evolved, which, in endeavouring to efcape, form ed cel!*, into which filiceous matter paffed by infd* tration, and formed agate. Thefe cells, he fuppofes, were filled, not by one, but from feveral fucceffi vC flony folutions, which depofited their contents, and thus formed thin coats of jafper, carnelian, chalce dony, &c. The infpedion of thefe agates fhews, that the fird precipitate has been the coarfeft, but that the fucceflive ones have continued to increafe in finenefs until out of the lad or fined foluticn amethyd h aS fliot, or w'hen it has had room enough has crydalh 2 ' cd. That the folution out of which thefe precipitate took place was truly chemical, is {hewn, not only by the appearance of the fubdances themfelves, but alfo by the mode of thejr depofition, as they follow accu rately the inequalities on the furface of the cavities, fo that an elevation on the interior wall continues to be obferved through all the fuperincumbent coats to the centre. When fpecimens of this kind are cut » l