Except in the coast belt, which is composed of superficial deposits, crystalline rocks are the fundamental for mation. From the edge of the coast belt to near the Niger-Benue confluence, these rocks are overlain by unfossiliferous sandstones, lying undisturbed, and possibly of the age of the sandstone of the Congo basin. Much of the plateau—with its flat-topped hills and red earths—consists of what is called the fluvio-volcanic series. The alluvial deposits here are often unconnected with the present drainage lines. On the Bauchi plateau are large deposits of cas siterite (tin) mostly found in the detrital deposits resulting from the great denudation over the plateau. Limestones, with fossils indicating a Tertiary age, have been found near Sokoto. Recent alluvium and a thick deposit of black earth border the upper reaches of the Benue and cover wide areas around Lake Chad. Coal measures are found in the Enugu district east of the Niger and south of the Benue, and in the Bende district near the Cross river ; there are large deposits of lignite in the younger Tertiary group in the Niger valley and in the neighbourhood of the Benue, where they are interstratified with white clays; rock phosphates are found north of Lagos and there is a belt of auriferous country north of Minna (towards the Kaduna river).
Though Nigeria lies wholly within the tropics, there is a distinct difference in the climate of the northern and southern regions. In the south the climate is typical of the tropics; in northern Nigeria it resembles that of Egypt and may be described as sub-tropical. In the south the temperature varies comparatively little, from 70° to oo° F, and averages over 80° F. The air is both hot and humid; the rainy season is sometimes prolonged to ten months or more, the rainfall in the delta being from i oo to 140 or more inches a year. (At Bonny in 1923 the fall was 150.59 in., rain occurring on 151 days.) The prevailing wet season wind is from the south-west. From November to March the harmattan, a dry, dust-laden north-east wind, coming from the Sahara, blows intermittently, and this ig the dry season, when at Lagos humidity has been known to fall to 26% against a mean of 9o%. At Lagos the usual rainfall is 77 in. a year. Tornados occur at the begin ning and end of the harmattan. Malaria is still a scourge in these southern districts and the country is unhealthy for Europeans. In the north the temperature is still high, but for nine months of the year the air is dry, "the dry air of the desert, the intense parching dryness of which is almost inconceivable by anyone who has not experienced it" (0. T. Faulkner, director of agriculture, Nigeria). July–September are the rainy months in the north, the fall being usually 25 to 3o in. a year, though in places it is as much as 6o inches. The harmattan begins in the north in October and lasts till April. In this season variations in temperature are great. At Hadeija, in 1922, a minimum of 35° F and a maximum of 115° F were recorded. In some parts of the plateau Europeans can live in comparative comfort, the climate resembling that of an un usually fine English summer, often with cool nights. Between the southern and northern regions there is an intermediate zone with a normal rainfall of from 4o to 5o in. a year and still considerable
humidity.
There are many large and small mammals. They include the elephant, lion, leopard, giraffe, West-African buffalo, many kinds of antelope and gazelle and smaller game. The chimpanzee, the drill ape, the baboon and many kinds. of monkeys are found in the forests and snakes are common. There are many varieties of squirrel, some finely coloured. The camel is found in the northern regions. In the rivers are rhinoceros, hippopotamus and crocodile. The manatus is also found. The birds include the ostrich, marabout, vultures, kites, hawks, ground hornbill, great bustard, guinea fowl, partridge, lesser bustard, quail, snipe, duck widgeon, teal, geese of various kinds, paraquets, doves, blue, bronze and green pigeons and many others. Domestic animals include the horse and donkey in the plateaux, but baggage animals are rare in the coast-lands, where the tsetse fly is found. Mosqui toes are abundant throughout the delta. There are the remarkable hammer-headed fruit-bat and other varieties of bats and a curious kind of dormouse. Many species of butterfly and spiders are recorded.
The mangrove is the characteristic tree of the swamps. North of the. swamps the oil palm (Elaeis guineensis) flourishes abun dantly. It is common as far as about 7° N. The evergreen and deciduous forests contain a great wealth of timber. Among the trees are mahogany, cedars and scented cedars, walnut, rosewood, satinwood, ebony, African teak and other valuable species. There are also African maple, shingle-wood, cork-wood, cotton-wood and other general utility woods, including the abura whose timber is acid resisting. Rubber vines are also found in these forests. Other trees found, chiefly on the plateaux, are the baobab, the shea-butter tree, the locust tree, gambier, palms, including the date and dum palm (Hyphaene), the tamarind, and, in the arid regions, the acacia and mimosa.
The vast majority of the inhabitants are typi cal negroes. In the south-west the Yorubas (q.v.) are the chief race. They occupy the country behind the coast-lands, from Da homey to Benin, and have a considerable degree of civilization. In the delta district and the forest zone, besides the people of Benin, are the Jekri, living on the lower part of the Benin river and akin to the Yorubas, the Ijos, living in the delta east of the main mouth of the Niger, and the Ibos, occupying a wide tract of country just above the delta and extending east from the Niger to the Cross river. South of the Ibos live the Aros, a tribe of relatively great intelligence, who dominated many of the surround ing tribes and possessed an oracle or juju of reputed great power. On the middle Cross river live the Akuna-kunas, an agricultural race, and in the Calabar region are the Efiks, Ibibios and Kwas. All these tribes are fetish worshippers, though Christian and Mus lim missionaries have made numerous converts. The Efiks, a coast tribe which early came into contact with white men, have adopted several European customs, and educated Efiks are employed in Government service. The great secret society called Egbo (q.v.) is an Efik institution.