An approximately circular complex 8 km in diameter is capped in places at higher levels by a roof of lavas and agglomerates. The principal rock types are syenites of widely varying grain size which vary from quartz- to nepheline- and analcime-bearing. Aegirine is the normal mafic mineral but some varieties contain augite, generally surrounded by sodic amphibole, and biotite. Within the southeastern part of the complex is an oval-shaped mass of 3x4 km of basement granite, gneiss and metavolcanics cut by numerous dykes. It is surrounded by a broad peralkaline syenite dyke. A small stock in the central area of the complex consists of umptekites containing a little nepheline and analcime; these pass into foyaites that are very much richer in nepheline. The volcanic rocks underlie a plateau about 3 km in diameter in the northeast of the complex. Basal agglomerates contain some trachybasaltic material, but they pass upwards into agglomerates and tuffs that are essentially of trachytic and latitic fragments. Radial solvsbergite-grorudite, bostonite and nepheline-bearing syenite dykes are widespread among the country rocks. Rock analyses are given by El Ramly et al. (1971), some trace element data for nepheline syenite by Ivanov et al. (1973) and U and Th data on three rocks are in El Reedy (1985).