In the area southwest of Hagar al Garda, and up to 50 km distance, there are a number of upstanding plugs. One such is 1.2 km in diameter and consists of trachyte but has a lenticular body of syenite within it which contains radiating aegirine needles. Some plugs apparently have trachytic margins but cores of porphyritic nepheline microsyenite containing eudialyte. Several circular structures of tilted ferruginous and silicified sandstones probably represent unexposed plugs. There are patches of pyroclastic rocks including trachytic agglomerates and tuffs and phonolitic tuffs associated with some of these structures (Hunting Geology and Geophysics Limited, 1974).