Common features of rock association, sequence of development and emplacement of rock units, form of complex, mineralogical and chemical characters, and the presence of quartzite blocks are explained as resulting from the uprise of volatile-rich basaltic magma being impeded by impervious structura traps of quartzite. It is suggested that the association of syenite with quartzite. alkaline basic igneous masses, and explosion-breccias is of genetic significance.