Within the limits of the tropical rains, the soil, rank from excessive heat and moisture, in some places is found covered with trees of most enormous size, encircled by kossom and other twining shrubs, which form bowers of a most beautiful description, enlivened by the notes of thousands of gaudy birds, and perfumed with fragrant aromatic breezes. These trees are often the acacia vera, or Egyptian thorn. They seldom grow above fifteen or sixteen feet high, then flatten; and, spreading wide at the top, touch each other, while the trunks are far asunder: and thus, under a vertical sun, for many miles together, there is a free space, in which both men and beasts may walk in a cool, delicious shade. Other parts of this region produce coarse grass, high enough to cover a man on horseback, or a jungle, composed of tall underwood and briers, which would be almost impervious to human beings were it not for the elephant and other large animals, which, crushing everything in their progress, form paths in various directions. In many places the land is highly cultivated, divided into plantations, fenced in as in England, possessing towns of more than thirty thousand inhabitants, and swarming with an immense population. Strangely contrasted with this picture of the wet portion of Africa are its dry, lifeless deserts, composed either of mountains and plains of hot stones, or of vast masses of loose, burning sand, which, sometimes formed into moving pillars by the whirlwind, and sometimes driven forward, like a mist, by the gale, threaten the traveller with death and burial, or, rather, with burial and then death; a fate which befell the army of Cambyses. In some places, however, the sand is found, like a layer of mortar, firmly cemented on the surface by an incrustation of salt; and it is in these scorching regions of salt and sand that the traveller experiences what he has emphatically termed "the thirst of the desert;" and yet, with all its horrors, the desert parts of Africa are more healthy, and afford a residence which is often more desirable than the rank, luxuriant regions; for the excessive rains bring into existence vast numbers of flies, moschetoes, and ants, which not only torment the body, but even devour the garments. Denham says (vol. ii., p. 91), "After a night of intolerable misery to us all, from flies and moschetoes, so bad as to knock up two of our blacks, we mounted, &c.... Another night was passed in a state of suffering and distress which defies description: the buzz from the insects was like the singing of birds; the men and horses groaned with anguish. I do not think our animals could have borne another such night." Besides producing these flies, the rains cover the country with extensive lakes, and, as far as the eye can reach, with immense miry swamps, which at first drive the wild beasts among the human race, and then putrify and corrupt the air; converting a verdant, smiling country into what may be termed a painted sepulchre.