250 QUARTZ FAMILY. remark, that the direction of the thin lamellar concretions of the menilite correspond with that of the slaty structure of the adhesive-slate in which it is imbedded. This fact shews that the menilite and slate are of cotemporaneous formation. Observations. 1. This subspecies is distinguished from the following, or the Grey Menilite, by its brown colour, its internal lustre, its more perfect conchoidal fracture, its translu- cency on the edges, its inferior weight, and geognostic situation. 2. It is nearly allied to Semi-opal; but it is distin guished from it by colour, shape, feebler lustre, inferior translucency, greater weight, and geognostic situation. 3. It was at one time arranged along with Pitchstonc, under the name Blue Pitchstone: more lately it has been described as a member of the Opal species, under the title Liver opal, (Leberopal). Werner first accurately de scribed it, and gave it its present place in the system. Second Subspecies. Grey Menilite. Grauer Menilite, Hoffmann. External Characters. Its colour is yellowish-grey, which sometimes inclines to wood-brown. It occurs tuberose, but more compressed than in the brown subspecies, and the external surface is smoother. Internally