The Marumbe complex is a small ring-intrusion consisting essentially of a plug of nordmarkite separated from the basalt country rocks by a later ring-dyke and roof-sheet of granite. The lower and upper surfaces of a screen of basalt, which lies between the top of the nordmarkite body and the base of the granite roof-sheet, correspond to successive horizontal fractures which permitted blocks limited by ring-fractures to subside as the nordmarkite and granite magmas were intruded. A series of sheets of granite are developed locally in the hanging-wall of the above-mentioned ring-dyke, and further granite ring-dykes cut the nordmarkite and the country rocks.