The specimen from the south side of the Capel Curig road, about ¼ mile from Beddgelert, which was collected by Mr. George G. Butler, and which he kindly placed at my disposal, is a rather dark greenish-grey rock, spotted with pale greenish-grey spherules, some of which are over ⅛ inch in diameter, and which, besides occurring isolated and in approximately spherical forms, have also coalesced, forming bands from ⅛ inch in breadth. On a smoothly cut surface they afford, by their pale tint, a strong contrast to the dark matrix. The isolated spherules and spherulitic bands are shown in fig. 3 (Pl. XXI.) as they appear when magnified about 6 diameters. A thin section, when examined between crossed Nicols, is seen to be studded all over with small doubly refracting specks. By ordinary transmitted light, and under a power of 25 diameters, a marked difference is visible in the microscopic characters of the spherules and the matrix, the former being almost colourless, save for a few pale greenish flecks, which become more closely aggregated at the margins of the spherules, forming a somewhat darker border, while the matrix appears to consist of a closely matted or granulated deep-green substance resembling chlorite, through which are interspersed a great number of clear spots consisting of nearly colourless matter, similar to that which composes the spherules. Between the spherules and the matrix, forming