It is a common feature of the dolerite dykes in Rhodesia, especially where they penetrate the great granite masses of the country, that they show, even in hand-specimens, the presence of quartz. Usually this quartz occurs in good-sized corroded fragments which are quite obviously xenoliths derived from the surrounding rocks. Of this a fine example is to be seen close to Bulawayo Railway Station, where a small dyke is at one point so full of quartz fragments, up to several inches across, as to resemble a conglomerate more than an igneous rock. Other parts of this same dyke and many other basic dykes throughout the country contain quartz, either in separate granules or in the form of micropegmatite, whose origin is not so clear. It is with a view to elucidating this point that the present notes have been put together. They deal entirely with two intrusions cutting the great Matopo granite mass. The relative ages of the dykes and the granite cannot be given in precise terms, as the data are much too imperfect.