[29] I do not know whether it is generally known, that bodies having exactly the same appearance as sphærulites, sometimes occur in agates. Mr. Robert Brown showed me in an agate, formed within a cavity in a piece of silicified wood, some little specks, which were only just visible to the naked eye: these specks, when placed by him under a lens of high power, presented a beautiful appearance: they were perfectly circular, and consisted of the finest fibres of a brown colour, radiating with great exactness from a common centre. These little radiating stars are occasionally intersected, and portions are quite cut off by the fine, ribbon-like zones of colour in the agate. In the obsidian of Ascension, the halves of a sphærulite often lie in different zones of colour, but they are not cut off by them, as in the agate. [30] _Journal de Physique,_ tome 59 (1804), pp. 10, 12. [31] _Idem,_ tome 60 (1805), p. 418. _Comparison of the obsidian beds and alternating strata of ascension, with those of other countries._—I have been struck with much surprise, how closely the excellent description of the obsidian rocks of Hungary, given by Beudant,[32] and that by Humboldt, of the same formation in Mexico and Peru,[33] and likewise the descriptions given by several authors[34] of the trachytic regions in the Italian islands, agree with my observations at Ascension. Many passages might have been transferred without alteration from the works of the above authors, and would have been applicable to this island. They all agree in the laminated and stratified character of the whole series; and Humboldt speaks of some of the beds of obsidian being ribboned like jasper.[35] They all agree in the nodular or concretionary character of the obsidian, and of the passage of these nodules into layers. They all refer to the repeated alterations, often in undulatory planes, of glassy, pearly, stony, and crystalline layers: the crystalline layers, however, seem to be much more perfectly developed at Ascension, than in the above-named countries. Humboldt compares some of the stony beds, when viewed from a distance, to strata of a schistose sandstone. Sphærulites are described as occurring abundantly in all cases; and they everywhere seem to mark the passage, from the perfectly glassy to the stony and crystalline beds. Beudant’s account[36] of his “perlite lithoide globulaire” in every, even the most trifling particular, might have been written for the little brown sphærulitic globules of the rocks of Ascension. [32] “Voyage en Hongrie,” tome i, p. 330; tome ii, pp. 221 and 315; tome iii, pp. 369, 371, 377, 381. [33] “Essai Géognostique,” pp. 176, 326, 328. [34] P. Scrope, in “Geological Transactions,” vol. ii (second series) p. 195. Consult, also, Dolomieu’s “Voyage aux Isles Lipari,” and D’Aubuisson, “Traité de Géogn.,” tome ii, p. 534.