Page:Africa by Élisée Reclus, Volume 3.djvu/531

 FLORA OF THE CONGO BASIN. 437 following the parallel river valleys of that region, while in the west, as far as and beyond the TJ-Banghi confluence, they are similarly changed to south-western or even western monsoons. They prevail especially in the dry season, acquiring their greatest intensity in September and March, that is, in the months preceding the two rainy periods. Thunderstorms are developed chiefly in the east, so that their progress is most commonly from the interior towards the Atlantic seaboard. As in the Gaboon and Ogoway valleys, there are two wet seasons, the first lasting from October to the end of December, the second and heavier from the middle of February to May, followed by an intensely dry period to the end of September, when scarcely a drop of water falls in a great part of the basin. But the rains diminish rapidly south of the Congo estuary, while increasing from the coast towards the interior. In the region of calms under the equator it rains throughout the year, although the principal wet season coincides here also with the winter months. In December, 1882, a violent thunderstorm was accompanied by a tremendous downpour of 4 inches within three hours, while in the disastrous years 1872 and 1874 the whole rainfall fell short of 8 inches, these remarkable droughts being followed by widespread famine. The fogs and overcast skies, caused by excessive moisture in the wet seasons, are often intensified by the conflagrations of the grassy steppes, where the com- bustion is calculated by Yon Danckelmann to represent a mass of 160 tons per square mile. Hence the quantity of scrub, brushwood, and vegetation of all kinds consumed by these fires must be estimated at millions of tons, filling the atmosphere with dense smoke for many miles in all directions. Flora and Fauna. Nevertheless the general absence of trees and prevalence of tall grasses in so many parts of the Congo basin is to be attributed not so much to these conflagra- tions as to the lack of sufficient moisture to support extensive forest growths. The dense woodlands of the Gaboon and Ogoway regions are gradually replaced southwards by treeless savannahs, except along the river banks, which are every- where fringed by narrow belts of timber, matted together by gigantic creepers. Even on the northern slope of the plateau forming the divide between the Congo and Zambese basins, the same contrast is presented between the treeless uplands and the exuberant vegetation of the riverain tracts. Here the more abundant moisture is carried off to the deep river gorges so rapidly that the rocky slopes and uplands are unable to support anything except a stunted and almost leafless scrub, or a scanty herbaceous vegetation, and are in some places even completely destitute of verdure. But at the issue of the parallel fluvial valleys south of the Congo, the abundantly watered plains are covered with palms, baobabs, and other large forest growths. Nearly all the semicircle limited north by the great curve of the main- stream and south by the Kassai and Sankuru rivers, presents the aspect of a boundless forest interrupted here and there by swampy tracts, savannahs, and the