MOCHA-STONES.
Moss-agates and Mocha-stones.—The beautiful siliceous pebbles called Moss-agates, and Mocha-stones, will so often come under the notice of the collector, that, although but extremely few, if any, of these objects contain organic remains, the arborescent substances they inclose being merely metallic oxides, a few remarks on their nature may be expected. The late Dr. Macculloch paid considerable attention to the investigation of these bodies, and believed that some of the objects imbedded in the pure and compact quartz were really of vegetable or animal origin; the specimen figured [Lign. 11] is of this kind; the fossils being apparently cellular cryptogamous plants. In Geol. Trans, vol. ii., other examples are figured and described by the same sagacious observer. Mr. Bowerbank is of opinion that spongeous structure enters into the composition of almost all the moss-agates, and I have no doubt that in some instances such organisms are present: but in by far the greater number of agates and mocha-stones the inclosed bodies are mere crystallizations; they are arborescent or dendritical oxides of manganese, copper, chlorite, iron, &c.
Lign. 10 Delesserites (Fucoides) Lamourouxii.
Monte Bolca. (Vég. Foss. Br.)
Lign. 11.
Moss and Conferva,
in transparent quartz, × 3.