Crust extracted from the mantle in arcs is refined into continental crust in subduction zones. During sediment subduction, subduction erosion, arc subduction, and continent subduction, mafic rocks become eclogite and may sink into the mantle, whereas more silica-rich rocks are transformed into felsic gneisses that are less dense than peridotite but more dense than the upper crust. These more felsic rocks rise buoyantly, undergo decompression melting and melt extraction, and are relaminated to the base of the crust. As a result of this process, such felsic rocks could form much of the lower crust. The lower crust need not be mafic and the bulk continental crust may be more silica rich than generally considered.