166 ME. <*. W. LAMPLTJGH OS THE [May I907, 



3000 feet above sea-level in a shallow valley through a country of 

 low relief. This country forms part of the great interior basin of 

 South Africa, whose featureless plains extend far to the northward, 

 westward, and southward ; ranging through some 20 degrees of 

 latitude, from beyond the watershed of the Congo nearly to the 

 Orange River ; and through 8 or 10 degrees of longitude, from the 

 rim of the west-coast slope to the valley of the Limpopo. Except 

 around a few clustered ' island-hills ' (Insel-bergen) the drainage- 

 gradients throughout this great basin are peculiarly low, and the 

 river-channels are only very slightly incised and present many 

 abnormalities. Dr. Passarge gives strong reason for believing that 

 the development of this plain has been due to prolonged and re- 

 current desert-conditions. That there have been important changes 

 of condition as regards rainfall and surface -drainage during and 

 since the development of the plain is evident, as Livingstone 

 and later travellers have recognized, from the character of the 

 superficial deposits ; the latest change in this, as in many other 

 parts of the world, having been one of progressive desiccation. 

 Prom his investigation of these deposits Dr. Passarge considers 

 that at some time previous to the setting-in of the recent desiccation, 

 there was a period of exceptional humidity in the region, probably 

 contemporaneous with the Glacial Epoch of higher latitudes, during 

 which the plain was watered by many rivers and lakes that have 

 now disappeared. But before this humid period there was, he 

 believes, a time of arid conditions ; and he interprets the evidence 

 as indicating also earlier cycles of alternation. 



Whatever its origin, this high-lying basin-plain, for the most 

 part deeply sand-covered, with its anomalous drainage-system, 

 constitutes the most striking feature in the physiographic structure 

 of Southern Africa. 



At the Victoria Falls, however, the broad Zambezi drops in a 

 single plunge from this region of low relief ; and .narrowing into a 

 deep and powerful torrent, hurries impetuously towards the Indian 

 Ocean. That a large volume of the drainage from the interior 

 must long have held this course is proved, as Mr. Molyneux has 

 pointed out, by the length and character of the trough which has 

 been excavated; the distance from the Falls to the lowermost of 

 the great gorges which these inland waters have carved out in 

 crossing the high eastern rim of the continent being nearly 600 

 miles, besides the further 350 miles of low country that is traversed 

 by the river before it reaches the ocean. The antiquity of the 

 interior plateau denoted by this great drainage-channel is indeed 

 significant. 



The country with which I have now to deal lies around the 

 highest of the gorges — the Batoka Gorge, as I have proposed to 

 name it. The strange zigzagging chasm just below the Victoria 

 Falls, into whose astonishingly narrow gullet the waters of the 

 Zambezi are gathered after their shattering plunge, has been 

 frequently described. In tracing the river eastward we found that 

 the gorge maintained its trench-like character for about 60 miles, 



