394 ME. T. CODKINGTON ON THE [Aug. I909,. 



seams of fine gravel. The islands, which are submerged by high 

 floods, are clothed with tropical vegetation and seem to consist 

 of alluvium like that in the banks of the river, probably on a 

 foundation of basalt. They are sometimes capped by pure white 

 sand, such as now comes down the rapids above. This sand, quite 

 unlike the coarser red cayenne-pepper-like sand, is found as far up 

 the Zambesi as the 16th degree of latitude, where Captain Bertrand. 

 pitched his camp 



' on an islet covered with white sand which squeaks under foot in a curious- 

 manner.' 1 



Mr. Lamplugh noticed the same in the Batoka Gorge, 



'beaches of glaring white quartz-sand, loudly "musical" when trodden on.' 2 



At a distance of 2 miles above the Falls smooth water ends, the- 

 river widens, and rocks and shoals and a succession of overfalls and 

 rapids, with intervals of stiller water and numerous islands, lead, 

 to the great cataract a mile in width. While the fall in the 

 surface of the water in the reach above is only a few inches per 

 mile, through the rapids below it is about 5 feet per mile, and on 

 nearing the Falls 16 to 18 feet per mile. The crest of the 

 Rainbow Fall is about 2885 feet above sea-level, which is 8 feet 

 higher than the bottom of the river at Livingstone Drift. 



The Falls themselves are but the last plunge of a cataract that 

 begins with the rapids 2 miles higher up, and the effect of the- 

 retrocession of the Falls is already felt thus far above them. 

 While the level of the water, whether the river is low or in flood, 

 falls with greater rapidity as it nears the Falls, the average 

 surface of the floor of the valley near the bank remains at about the 

 same level. Deep channels in the river-bed are already eroded ;. 

 one a mile above the Falls, 36 feet deep and about 20 feet below 

 the crest of the Falls, has been proved to exist near the left bank, 

 and there are probably others quite as deep. 



Low water under the bridge spanning the gorge below the Falls- 

 is 2521 feet above sea-level, which is 364 feet lower than the 

 crest of the Rainbow Fall ; allowing 6 feet for the fall in the water- 

 level to the bridge would make the height of the Falls 358 feet. 

 The observed difference between low water and flood-level in the 

 gorge at the bridge is 56 feet, and for a mile and a half below 

 the bridge the gradient of the surface at low water is 17 feet 

 per mile. 



Along the course thus sketched, a tranquil reach between rapids r 

 flows a river which has an annual flood rising gradually from 

 November or December to April or May, and falling for the 

 succeeding six or seven months. Below the confluence of the- 

 Linyanti, some 45 miles above the Victoria Falls, where the water- 

 level is stated to be 3210 feet above the sea, the flood is said to 

 rise 20 feet. 3 In the reach above the Yictoria Falls, according to- 



i 'The Kingdom of the Barotsi' 1899, p. 166. 



2 Quart. Journ. Geol. Soc. vol. lxiii (1907) p. 205. 



3 A. St. H. Gibbons, Geogr. Journ. vol. ix (1897) p. 121. 



