Coralliform Quartz

Having shown some modifications in Limestone and Flint separate, it becomes somewhat necessary to show them in different substances; and the more so, as they have not been noticed by mineralogical writers. Varieties of the present sort of specimen have been taken for roots of different plants, as Ferns, &c. It is, however, another sport of Nature, forming the imitation of one substance which is imbedded in another. Thus the Coral is chiefly Quartz, and is imbedded in argillaceous Limestone. The Quartz in the polished piece is indicated by its taking a better polish than the Limestone; for what polishes Quartz grinds the Limestone, and will not give it a smooth surface; and the specimen having been thrown about as a boulder in the bed of some river, the Quartz is left beyond the Limestone, resembling stumps of plants, in many instances not much unlike stubble in a lump of earth encompassing the roots. I have received pieces from the shore of North Wales, This kind nearly resembles Madrepora musicalis of Linnæus, figured Esper 1. Madrep. tab. 30.