This large recent volcanic field extends into Uganda (where it forms the Bufumbira field - see Uganda No. 7) and Rwanda (Rwanda Nos 1-6), but the greater part is within Congo in the Western Rift. There are eight lofty volcanic peaks within the field the highest of which is Karisimbi (4507 m) (No. 12, but see also Rwanda No. 5). The two most westerly volcanoes Nyamuragira (No. 7 ) and Nyiragongo (No. 8 ) have been almost continuously active since the area was first visited by Europeans in 1894, but it is likely that all the volcanoes, with the possible exception of Mikeno (No. 9) which is deeply eroded, are dormant. Apart from the central volcanoes the volcanic rocks have also erupted from numerous satellite centres Nyiragongo alone having nearly 100 satellite cones. Two of the central volcanoes, Karisimbi and Visoke, straddle the border with Rwanda, while Sabinyo makes a triple border junction between Congo, Rwanda and Uganda. Within Congo the volcanic rocks cover a rectangular area of 60x40 km with a narrow arm extending some 40 km to the northwest. A general account of the geology and geomorphology, although with the main emphasis on Uganda, is given by Combe and Simmons (1933). Collected rock analyses for the whole field, with brief petrographic notes, are available in Denaeyer et al. (1965) and in a supplement by Denaeyer (1972), while others will be found in Holmes and Harwood (1937). A detailed geology map on a scale of 1:50,000 for the Nyiragongo and Nyamuragira parts of the field is that of Thonnard and Denaeyer (1965).