INTRODUCTORY OBSERVATIONS. 9 Diorite (Greenstone). A crystalline granular rock composed of felspar and hornblende. Magnetite in small opaque crystals is generally present. (The diorites are generally found as intrusiv e masses amongst the older Palaeozoic formations.) Minette (Mica-trap). A felsitic base with much mica; distinct crystals of orthoclase, and sometimes of hornblende, are present in some specimens. (Minette generally occurs in dykes amongst the older Palaeozoic rocks.) TEETIAEY AND MODERN VOLCANIC BOCKS. I. Crystalline. (Basic.) Basalt. A micro-crystalline compound of Labra- dorite, augite, and titano-ferrite or magnetite, gene rally black or dark green. Olivine is frequently present. Basalt occurs in dykes or sheets. Dolerite. A largely crystalline rock of the same composition as basalt. An intermediate stage is sometimes called ‘ anamesite.’ Leucite Rock. A crystalline-granular compound of leucite and augite, with magnetite, porphyritic or compact. (Mr. S. Allport has discovered this mineral in the Wolf Eock, off the coast of Cornwall.) Hyperstiiene Eock. Crystalline granular com pound of Labradorite and hypersthene with titano-