The oldest Precambrian rocks in Ghana, referred to the Dahomeyan, were subdivided in 1945 into four groups of gneisses, two basic and two acid. In the western basic gneiss belt, about 10 percent of the rock consists of veins with plagioclase, scapolite, hornblende, and garnet, as in the gneiss, but a greater proportion of light minerals. The gneissic mineral banding persists through the veins and either the veins were in the rock before the banding was imposed, or they are replacement veins. As the intense movement necessary to produce the banding would have destroyed any veins, it is concluded that they were formed by large-scale replacement. The veins have been studied chiefly in the Shai hills area, northeast of Accra.