Several volcanic centres in the east of the country were active during the Cenozoic. The carbonatites and nephelinites, lavas and agglomerates together with lahar deposits are collectively referred to as the Elgon Complex after Mount Elgon, the principal eruptive centre. Sediments of the Albertine Supergroup which include lavas, tuffs, silts, sands and gravels are found widely deposited within the Western (Albertine) Rift. The basalts and other deposits of the Bufumbira Formation occur in the southwestern extremity of the country. Nephelinites and basalts collected together as the Ngenge Formation are distributed in the Mount Elgon area and northwards. Superficial deposits of the last few million years include widespread development of laterites and deposition of alluvial sands and gravels by rivers.