A Small series of rock-specimens, consisting chiefly of fragments of basalt, dolerite, volcanic conglomerate and tuff, which were collected near Kilima-njaro, by F. Holmwood, Esq., C.B., lateConsul-General at Zanzibar, was recently forwarded to the Museum at Jermyn Street, and placed by Dr. A. Geikie in my hands for determination. Among these specimens was a small block, the crystalline texture and high density of which at once arrested attention Freshly fractured surfaces of this rock present numerous glistening facets, which with the aid of the pocket-lens are seen to be the cleavagefaces of a yellowish-green, a dark-green, and a garnet-red mineral. These minerals are respectively olivine, hornblende, and hypersthene in nearly equal proportions, the hornblende being perhaps slightly predominant. They form a holocrystalline granular aggregate, in which the.grains are of nearly equal size and without crystalline contours; in other words, the structure is allotriomorphic-granular. Subordinate both in size and quantity to the three principal constituents is magnetic iron-ore.