Plutonic rocks of acid composition are very extensively developed in Africa south of the Equator. These rocks present many features of interest, and, especially under the microscope, many minerals may be recognized besides the usual quartz, felspar, and ferromagnesian constituents. Thus the granite of Cape Town itself is remarkably rich in accessories. Tourmaline, in particular, is very abundant in places. In thin sections it is of a yellowish brown colour frequently bordered and zoned with pale blue, while some crystals show alternate bands of yellow and brown. Cordierite also appears to be sometimes present in the normal granite. It may be quite fresh and almost indistinguishable from quartz, while in other cases it is entirely replaced by the yellowish micaceous ‘pinite’ pseudomorphs. The intermediate stages of the alteration are well shown, while it is interesting to note that it seems to have crystallized sometimes before and sometimes after the felspar.