The universal geography : earth and its inhabitants

20
WEST AFEICA.
uplands throuj^hout tbo whole year. The other elevated lands on this seaboard
also receive u large share of the rainfall, which is nowhere heavier in anj^ part of
the Atlantic than in this oceanic region exposed to the influence of the north-eaat
and south-east trade winds between the projecting coasts of West Africa and South
America. Here the still air arrests the rain-clouds brought by both trade winds,
the vapours are condensed and precipitated in tremendous downpours on the
subjacent waters. In many jjlaces this rain water, owing to its less specific
Fig. —CUEICENTS OF niE SoUTH AtL.INTIC .\N1) LiXES OF IcEBEEOS.
Scale I : 87,000,000.
1,200 Miles.
gravity, spreads over the .surface in sufficiently tliiclc layers to enable passing
vessels to replenish their supply of fresh water.
Although incessantly intermingled by the aerial and marine currents, the
waters of (he iVtlantic ba.sin differ none the less in their degree of salinity not only
on the surface, but also in the deeper strata. The most saline is that encircling
St. Helena, the specific gravity of which is 1-0285. Owing to the heavy rains in
the region of calms tlie proportion is less in the Guinea Stream, the difference
being as much as two or even three thousandths in the north-east part of the