Yol. 6^."] GEOLOGY OF THE ZAMBEZI BASIN. 167 



and then rather suddenly expanded into a more open valley. The 

 geological structure of the country remained unchanged, however, 

 up to Makwa l or Wankie's Drift, the eastward limit of our journey 

 along the Zambezi, several miles below the termination of the 

 gorge ; where we were still on the same plateau-basalts which we 

 had traced uninterruptedly from the Falls. Through its great 

 trench the river pours tumultuously, like an overgrown mountain- 

 torrent, fretted at short intervals into foaming rapids, and at 

 the season of low water in places confined within rock-bound 

 gullies sometimes not more than 20 or 30 yards in width ; but in 

 such places bordered by wide platforms of bare rock, deeply 

 indented with ' pot-holes,' over which the enormously augmented 

 stream is poured in flood-time. The difference between the volume 

 of the river during low water and during the floods must indeed be 

 great ; since we saw indications, where the bottom of the gorge was 

 narrow, that the river rises at least 50 feet above its dry-season 

 level. It is to the effect of this extreme seasonal variation upon 

 certain structural peculiarities of the basalts, presently to be 

 described, that the characteristically acute swerves of the river 

 within its gorge are to be attributed. 



The Zambezi at the Victoria Falls loses at once 360 feet of 

 altitude, but this is only the first great step in its rapid descent; for, 

 by the time that it reaches Makwa, after its emergence from the 

 Batoka Gorge, it appears to have lost at least a further 800 or 900 

 feet. 2 And although the basaltic plateau itself declines eastward, 

 the river falls more rapidly in this direction ; so that the depth of 

 the canon is increased from about 400 feet near its beginning to 

 about 800 feet (by aneroid measurement) at the spot where I 

 descended into it a few miles above its termination. As I have else- 

 where discussed the indubitable evidence for the gradual develop- 

 ment of the Gorge by erosion, it is needless for me to recapitulate the 

 points. The photographs reproduced in Plates X-XIV, selected to 

 show the features of the canon at different parts of its course, will 

 also suffice to illustrate one of these points, to wit, the progressive 

 reduction eastward in the steepness of its sides, from verticality 

 in the newly-cut portion at the Falls to slopes of 30° or under in 

 the older portion which has suffered prolonged weathering. 



1 I have found that so much confusion arises from the repetition of Wankie 

 or Wankies as a place-name in the district formerly ruled by the chief, 

 Wankie or Tzwanki, that I propose hereafter to restrict the use of the name 

 to the place where the coal-mine, railway-station and post-office are 

 established, and to adopt Major A. St. H. Gibbons's term, Makwa, for 

 Wankie's Drift or Ferry across the Zambezi. The old chief was much harried 

 by the Matabeli, and had several times to shift the site of his settlement, so that 

 there are still three or four places bearing his name. The nomenclature of the 

 country, however, at present stands in need of revision in many particulars. 



2 This estimate is based on my aneroid observations ; it is borne out by the 

 figures given by Mohr (' To the Victoria Falls of the Zambesi ' 1876, p/329) 

 for the height above sea-level of Wankie's village [Makwa] — 1680 feet ; and by 

 Baines for the level, of his camp at Logier Hill — 1550 feet (' The Gold Eegions 

 of South-Eastern Africa ' London, 1877, p. 187). 



