- Class 2. Earths.
- Order 2. Mixed.
- Lithomarga. Kirw. 1. 187.
- Argile lithomarge, Argilla crustacea. Waller, 1. 49.
- Stein-mark. Emmerl. 1. 355.
- La Moelle de Pierre, ou la Lithomarge. Broch. 1. 447.
The substance which I find generally termed Lithomarga seems to be an argillaceous Steatite or Stcatitic Clay. I gather this from the descriptions in different authors, although some are doubtful as to its containing Steatite or Magnesia, which generally gives an additional soft or soapy quality to it. The present specimens are from near Keswick in Cumberland, The provincial name is Moidal.—It more or less adheres to the tongue as it is loose, or indurated, and some parts of these specimens are more so than others. The Lithomarga feels smooth, with a slippery softness, its looser parts soiling the fingers and the harder parts not, the former readily making a streak on paper or any such substance.
The vulgar idea of Rock Marrow seems curiously analogous to the upper specimen, which resembles the bone also; the lightish part representing the latter and the darker the marrow*. It resembles a soft Slate, and we sometimes find veins in Slate much resembling the lighter part; the central figure is little else, coated with the grey variety as in the middle of the upper one, which just passes into the whiter part in small dendritical figures. They are both found near a slate quarry. The lower specimen is from Silver-bourn in the Isle of Man, where Lord James Murray informs me it is found in plenty. I do not know that any use has been made of it; when fresh it was hoped that it might serve as Fuller’s Earth.
- * This somewhat agrees with the description of the Rock-Soap of some authors.