THE RAINY SEASON. 445 



were a portion of the original bottom, and fossils may yet 

 be found in them.* 



The characteristics of the rainy season in this wonder- 

 fully humid region, may account in some measure for 

 the periodical floods of the Zambesi, and perhaps the 

 Nile. The rains seem to follow the course of the sun, 

 for they fall in October and November when the sun 

 passes over this zone on his way south. On reaching 

 the tropic of Capricorn in December, it is dry ; and 

 December and January are the months in which in- 

 jurious droughts are most dreaded near that tropic (from 

 Kolobeng to L,inyanti). As he returns again to the north, 

 in February, March, and April, we have the great rains 

 of the year ; and the plains, which in October and No- 

 vember were well moistened, and imbibed rain like 

 sponges, now become supersaturated, and pour forth those 

 floods of clear water which inundate the banks of the 

 Zambesi. Somewhat the same phenomenon, probably, 



* After dwelling upon the geological structure of the Cape Colony 

 as developed by Mr. A. Bain, and the existence in very remote periods 

 of lacustrine conditions in the central part of South Africa, as proved by 

 freshwater and terrestrial fossils, Sir Roderick Murchison thus writes : — 



" Such as South Africa is now, such have been her main features 

 during countless past ages, anterior to the creation of the human race. 

 For the old rocks which form her outer fringe, unquestionably circled 

 round an interior marshy or lacustrine country, in which the Dicyno- 

 don flourished, at a time when not a single animal was similar to any 

 living thing which now inhabits the surface of our globe. The present 

 central and meridian zone of waters, whether lakes or marshes t 

 extending from Lake Tchad to Lake 'Ngami, with hippopotami ore 

 their banks, are therefore but the great modern residual geographical 

 phenomena of those of a mesozoic age. The differences, however, 

 between the geological past of Africa and her present state, are 

 enormous. Since that primeval time, the lands have been much 

 elevated above the sea-level — eruptive rocks piercing in parts through 

 them ; deep rents and defiles have been suddenly formed in the sub- 

 tending ridges through which some rivers escape outwards. 



"Travellers will eventually ascertain whether the basin-shaped 

 structure, which is here announced as having been the great feature of 

 the most ancient, as it is of the actual geography of South Africa {i.e. 

 from primeval times to the present day), does, or does not, extend into- 

 Northern Africa. Looking at that much broader portion of the 

 continent, we have some reason to surmise that the higher mountains 

 also form, in a general sense, its flanks only." — p. cxxiii. President's 

 Address, Royal Geographical Society, 1852. 



