It includes a variety of high-grade metamorphic rocks both sedimentary and igneous in origin. The dominant lithology is gneiss with minor mafic and ultramafic intrusives. Metamorphism is mainly of the almandine amphibolite facies, rarely reaching the granulite facies. It occurs south and east of the Archean craton. Granulites and biotite gneisses of pelitic origin make up a larger portion of the unit.
Structural trends are dominantly to the southwest.
Rocks of granulite facies of the Ubendian and Usugaran Systems are rich in a variety of colored gemstones. Karagwe-Ankolean System . This system extends west of Lake Victoria. It is younger than the Ubendian and Usagaran. The granites have alteration haloes containing tin and tungsten mineralization in veins.