The author, after alluding to his former papers on the fluids in topaz, described, in Section I., the form and position of the strata in the minerals in which the cavities occur. They generally occur in immense numbers, occupying extensive strata, and injuring the transparency of the mineral. These strata occupy every possible position, and have every possible curvature; their shape is equally irregular; and it is probable that, in every case, some edge or angle of the stratum touches the surface.