To the presence of mangrove trees must be attributed, in part at least, the unhealthy character of the estuaries of African rivers. From the roots, when left bare by the tide, a sickly odour arises; and the vicinity of a mangrove forest is always exposed to the deadly malaria. "The shore," says Kingsley, describing a mangrove forest, "sank suddenly into a low line of mangrove wood, backed by primeval forest. The loathsome floor of liquid mud lay bare beneath. Upon the endless web of inter-arching roots great purple crabs were crawling up and down. The black bank of dingy leathern leaves above; the endless labyrinth of stones and withes (for every bough had lowered its own living cord, to take fresh hold of the foul soil below); the web of roots, which stretched far away inland; —all seemed one horrid, complicated trap for the voyager: there was no opening, no relief—nothing but the dark ring of mangroves, and here and there an isolated group of large and small, parents and children, bending and spreading, as if in hideous haste to choke out air and sky. Wailing sadly, sad-coloured mangrove-hens ran off across the mud into the dreary dark. The hoarse night-raven, hid among the roots, startled the voyager with a sudden shout, and then all was again silent as the grave."

In the rivers of Africa the terrible crocodile takes the place held by the alligator in America. There also we encounter the hippopotamus and the still more frightful rhinoceros. Herds of elephants may be seen winding through the open plains, swimming across the rivers in majestic lines and with elevated trunks, or bathing in the shallow lakes for coolness or protection against insects. The antelope (of which Africa is the special nursery), the giraffe, the buffalo, the zebra, are all found in abundance in the plains of southern and central Africa, from Orange river in the south to the Senegal and Nubia in the north.