In a paper read before the Royal Society in 1885, allusion was made to certain greyish, or yellowish-white spherulites occurring in a specimen of black obsidian which was given me by the late Mr. John Arthur Phillips, F.R.S. These spherulites (portions of two occur in the specimen) are about an inch in diameter and are seen to consist of numerous spherulites of very much smaller dimensions. In the paper referred to it was suggested “that the smaller spherulitic structure was set up in the large spherule after its formation, the vestiges of a radiating crystalline structure tending to confirm this view.” This opinion was based merely upon what could be seen on a fractured surface by the help of a pocket-lens. The microscopic examination of a section made through one of these bodies seems, however, to show that the smaller spherulites were formed first, and that after they had assembled together in spheroidal aggregates, a radiating crystallization was set up within the mass, travelling stage by stage from the centre to the periphery. As I have not yet met with any account of precisely similarspherulites, even in Mr. Iddings's monograph, it seems to me that the following notes may prove of some interest to petrographers. In reflected light, but better when dark-ground illumination is employed the entire section of the spherulite is seen to be composed of much smaller spherical or spheroidal bodies, so closely packed that they are usually in contact, the matter occupying the interstices appearing darker than