A description is given of the geology of the northern portion of the Ruwenzori Mountains. The rocks consist chiefly of a migmatitic series of biotite-gneiss passing to plagioclase-amphibolite uncomformably overlying these are rare occurrences of a slightly metamorphosed series of conglomerates, grits, quartzites, and tale-schists. The area is bounded by rift faults which strike N.N.E.– S.S.W. and the strike of the gneiss series is in general parallel to that direction with a steep westerly dip. Major rift faults arc described and evidence given to show that they are rejuvenations of Pre-Cambrian fault lines. Dextral tear-fault movement is implied with superimposed vertical component. Evidence indicates that faulting took place under compressional stress in Pre-Cambrian times, but that tension supervened at the later stages under light load. A steeply dipping faulting system striking W.N.W.–E.S.E. is also present, and has resulted in the southern blocks rising relative to the northern: in this system also, early compressional stress has been superseded by tension.