XXI. Account of a Variety of Argillaceous Limestone, found in connexion with the Iron-stone of Staffordshire.

Abstract

The variety of limestone here referred to is called by the miners Curl . The name evidently alludes to the convoluted form of its distinct concretions, each of which is either itself a complete and regular cone, or is wrapped round part of a cone, which serves as the basis of its structure. Each distinct concretion, on being parted from the conical surface to which it has been attached, presents on its concavity a series of wrinkles, regularly indented, and always parallel to the base of the cone. The convex surface is longitudinally striated. The circular bases of the cones project a little one beyond another, and thus give to the external surface of the mass the appearance of leaves folded over one another. Hence has arisen the conjecture, that the mineral in question is a petrified palm, or lotus. This opinion would have been immediately abandoned, if those who adopted it had descended into the bowels of the earth to see the substance in its natural situation, instead of merely inspecting the detached masses of it, which, in the neighbourhood of Cosely, are seen on every side, lying upon the ground, or used in building walls. The fracture of this mineral is splintery; its colour greyish black. The masses, which are exposed to the weather, soon acquire externally a yellow rusty aspect, from the combination of oxygen with the iron which they contain. The curl is here found in connexion with one stratum only. This is a bed of iron-stone,