found a great quantity of a brown, arborescent substance adhering to some trap-rock. In its arborescent form, this substance singularly resembles some of the branched species of Nullipora. Under the blowpipe, it behaves like the specimens from Ascension; but it is less hard and glossy, and the surface has not the shrunk appearance. CHAPTER III. ASCENSION. Basaltic lavas. Numerous craters truncated on the same side. Singular structure of volcanic bombs. Aeriform explosions. Ejected granitic fragments. Trachytic rocks. Singular veins. Jasper, its manner of formation. Concretions in pumiceous tuff. Calcareous deposits and frondescent incrustations on the coast. Remarkable laminated beds, alternating with, and passing into, obsidian. Origin of obsidian. Lamination of volcanic rocks. (MAP 2: THE ISLAND OF ASCENSION.) This island is situated in the Atlantic Ocean, in latitude 8 degrees S., longitude 14 degrees W. It has the form of an irregular triangle (see Map 2), each side being about six miles in length. Its highest point is 2,870 feet (“Geographical Journal” volume 5 page 243.) above the level of the sea. The whole is volcanic, and, from the absence of proofs to the contrary, I believe of subaerial origin. The fundamental rock is everywhere of a pale colour, generally compact, and of a feldspathic nature. In the S.E. portion of the island, where the highest land is situated, well characterised trachyte, and other congenerous rocks of that varying family, occur. Nearly the entire circumference is covered up by black and rugged streams of basaltic lava, with here and there a hill or single point of rock (one of which near the sea-coast, north of the Fort, is only two or three yards across) of the trachyte still remaining exposed. BASALTIC ROCKS.