530 G. W. Lamplugh—The Victoria Falls. 



earth's crust is inadequate to explain the phenomena observed around 

 the Falls, while all the features are compatible with the view that 

 the river has slowly sunk its channel into the hard rocks which 

 have barred its passage seaward ; and that the great waterfall has 

 been developed as an incident in its long-continued work of erosion. 

 A recent geological investigation of the country on both sides of 

 the Zambesi between the Falls and the Deka Kiver, about 70 miles 

 eastward, has yielded much evidence confirmatory' of Mr. Molyneux's 

 conclusions, of which we can here give only the barest outlines. 



It will be remembered that the Upper Zambesi flows, with a com- 

 paratively gentle course, over a portion of the elevated plateau of 

 South-Central Africa, and that when it reaches the vicinity of the 

 Falls its bed is still about 3,000 feet above sea-level. But at this 

 point it breaks sharply away from its earlier habit, to begin a rapid 

 descent across the mountainous eastern margin of the continent, and 

 in doing so its capacity for erosive work is, of course, enormously 

 increased. From the Falls onward until it reaches the coastal plain 

 about 260 miles from the sea, the river has sunk its channel deeply 

 through evei'y obstacle, carving out narrow defiles like the Lupata 

 Gorge, the Kebrabasa Gorge, the Kariba Gorge, and the canyon 

 below the Falls, to which the name Batoka Gorge may be applied, 

 wherever the rocks in its course are hard and resistant ; and 

 excavating a wider and less precipitous valley where it crosses the 

 outcrop of strata that perish more readily. 



The whole of the country for many miles on both sides of the 

 Zambesi between the mouth of the Deka and Victoria Falls, and also 

 for a considerable distance farther westward is occupied by hard 

 basaltic rocks, the ' Batoka Basalts ' of Molyneux, which have been 

 poured out over the land as flows of liquid lava at some remote 

 period of which the exact position in the geological time-scale has 

 not yet been definitely ascertained. Scarcely was one of these 

 lava-flows consolidated before it was overwhelmed by another, and 

 still another, until the whole area surrounding this part of the course 

 of the present Zambesi was covered to a depth of many hundreds, 

 in places perhaps many thousands, of feet of volcanic material. The 

 slowly-cooled central portions of these separate lava-flows have 

 consolidated into the dense dark-blue rocks weathering with a brown 

 crust that are so well seen in the precipices of the existing Falls, 

 while their more quickly cooled slaggy upper portions, once porous 

 with empty steam-cavities, have formed the deep red or purple 

 ' amygdaloidal ' bands that are rendered conspicuous to the eye, and 

 very interesting to the mineralogist, by the varied minerals deposited 

 by percolating waters. B}' this agency the cavities have been 

 gradually filled up with the beautiful agates, green-coated chalcedony, 

 quartz-crystals, and zeolites that may now be picked up so abundantly 

 at the surface along the outcrop of these amygdaloidal rocks. And 

 it may here be mentioned as of some interest to the archgeologist 

 that the chalcedonic pebbles have been frequently chipped to form 

 rude cutting tools by some ancient race inhabiting the Zambesi 

 valley, these relics of ancient man being especially numerous on the 



