thus have acquired their different textures. [24] “Geological Transactions,” vol. 3, part i, p. 37. [25] The foregoing analyses are taken from Beudant “Traité de Minéralogie,” tome ii, p. 113; and one analysis of obsidian from Phillips’s “Mineralogy.” [26] These analyses are taken from Von Kobell’s “Grundzüge der Mineralogie,” 1838. [27] “Traité de Géogn.,” tome ii, p. 535. [28] This is seen in the manufacture of common glass, and in Gregory Watts’s experiments on molten trap; also on the natural surfaces of lava-streams, and on the side-walls of dikes. The natural sphærulites in these rocks[29] very closely resemble those produced in glass, when slowly cooled. In some fine specimens of partially devitrified glass, in the possession of Mr. Stokes, the sphærulites are united into straight layers with even sides, parallel to each other, and to one of the outer surfaces, exactly as in the obsidian. These layers sometimes interbranch and form loops; but I did not see any case of actual intersection. They form the passage from the perfectly glassy portions, to those nearly homogeneous and stony, with only an obscure concretionary structure. In the same specimen, also, sphærulites differing slightly in colour and in structure, occur embedded close together. Considering these facts, it is some confirmation of the view above given of the concretionary origin of the obsidian and natural sphærulites, to find that M. Dartigues,[30] in his curious paper on this subject, attributes the production of sphærulites in glass, to the different ingredients obeying their own laws of attraction and becoming aggregated. He is led to believe that this takes place, from the difficulty in remelting sphærulitic glass, without the whole be first thoroughly pounded and mixed together; and likewise from the fact, that the change takes place most readily in glass composed of many ingredients. In confirmation of M. Dartigues’ view, I may remark, that M. Fleuriau de Bellevue[31] found that the sphærulitic portions of devitrified glass were acted on both by nitric acid and under the blowpipe, in a different manner from the compact paste in which they were embedded.