On the Cup-shaped Joints in Prismatic Basalt

Abstract

THE difference between Mr. Mallet (NATURE, vol. xiii. p. 7) and myself is simply this. He asserts, as necessary to his theory, that the “convexities” should always project in the direction in which the cooling and consequent “splitting is proceeding” (“Proceedings of the Royal Society,” No. 158, p. 182). I referred him to the beautiful specimen, in the hall of the Geological Society's Museum, of three columns, one of which exhibits an articulation in the shape of a double-concave lens; the adjacent convexities consequently pointing, in this case, in opposite directions.