Observations on Basalt, and on the Transition from the vitreous to the stony Texture, which occurs in the gradual Refrigeration of melted Basalt" with some geological Remarks. In a Letter from Gregory Watt to theRight Hon. Charles Greville. Read May 1.

(London, W. Bulmer and Co., 1804). 4to. No wrappers as extracted from "Philosophical Transactions" 1804 - Part II. Pp.279-314. First appearance of the paper in which Watt set forth his "Crystallization Hypothesis"."The first hypothesis as to the origin of prismatic structure which which had any experimental or observational basis was that of Gregory Watt, and may be entitled "crystallization hypothesis". Whatt in 1804 observed (the paper offered) that a large mass of basalt which he had melted down in a reverbatory furnace crystallized radially from centers which were fairly regularly spaced in a horizontal plane" the intersections of these radially growing fibrous bundles formed a network of hexagonal partings through the mass, leading Watt to the conclusion that this manner of crystallization, by its vertical extension upward from the base of a mass of basalt, must have been the cause of the prisms found in the Giant's Causeway, Fingal's Cave, and elsewhere." (Robert B. Sosman in "Types of Prismatic Structure in Igneous Rocks", p. 215).…