In a former communication to this Society, I have demonstrated that quartz must now be added to the long list of minerals in which a lamellar structure can be set up by mechanical stresses. In that paper, a crystal of smoky quartz was described in which well marked lamellæ could be detected; the relations of these lamellæ to the parts of the crystal which had suffered mechanical deformation and crushing are such as to leave no possibility of doubt that the lamellar structure is not an original but a secondary one; while it is equally clear that the structure has been developed by the action of mechanical forces upon the crystal.