May 25, 1857.] SOUTH AFRICA— LIVINGSTONE. 449 



Africa would be found to be a comparatively low, watery expanse, 

 tbe rivers issuing from wbich escaped to the east or to the west 

 through gorges or rents in the subtending higher chains, was proved 

 to demonstration by Livingstone, as respects that vast African river, 

 the Zambesi. 



The observations of this great traveller afford also the proof 

 that several of the principal rivers of Africa south of the equator 

 have their sources in comparatively level tracts of no great altitude. 

 Just as the great rivers of Russia are separated at their sources by 

 water-partings of such slight altitude, that Peter the Great connected 

 these diverging streams by canals, so Dr. Livingstone has observed 

 analogous phenomena in the heart of Africa. The African case is, 

 indeed, still more remarkable. In this region Nature herself has 

 made the connecting canal ; for flat boats and canoes can pass north- 

 wards by the Dilolo river into the affluents of the Congo or Zaire 

 on the west, and into the Zambesi on the east. 



These humid regions, particularly towards the west side of the 

 continent, are covered by lofty forest trees, abundance of ferns, mosses, 

 and other plants requiring much moisture. Hence the explorations 

 of Livingstone, opening out such new and unexpected data, induce 

 me to put a question for solution by physical geographers. Why 

 does it happen, that whilst moisture so prevails in lats. 10° to 15° 

 south of the equator, the same districts equally distant from that 

 line upon the north (as touched upon by Earth) should be arid and 

 comparatively dry ? After such positive data as those collected by 

 Livingstone, we have indeed no longer occasion to stretch the ima- 

 gination and suppose the existence of great snowy mountains from 

 which the waters of the Nile take their rise ; since we now see that 

 the Zambesi and the Congo are supplied from marshes at lower 

 levels than the chains through which those streams escape. The 

 simple fact is, that in Central Africa there are two copious rainy 

 seasons due to the periodical influence of the sun, the passage of 

 which is accompanied by copious torrents. By the first of these 

 rains the boggy lands become to a great degree saturated, but the 

 water not overflowing, finds no exit in the absence of an adequate 

 declivity. It is only when the whole spongeous mass becomes 

 supersaturated by the second rains, that the waters rising to a great 

 height, furnish the Zambesi with its annual flood. 



In like manner the Nile may owe its annual flood to a similar 

 cause — a point which, can only be determined when our bold ex- 



