G. W. Lamplugh — The Victoria Falls. 531 



patches of old river-gravel that are exposed around the low rocky 

 bosses of the low ground in the vicinity of the northern bank of 

 the rivei", in the angle between the Zambesi and its tributary, the 

 Maramba. 



The Batoka lavas in consolidating to their present state have 

 developed a system of joints or shrinkage cracks which, together 

 with rarer but more strongly marked lines of fracture or ' faulting,' 

 have constituted planes of weakness that have materially facilitated 

 the erosive work of the river, just as they would be found to 

 facilitate the operations of artificial quarrying. Both ' master-joints' 

 and 'faults' for the most part run approximately west and east, and 

 are mainly accountable for the apparent vagaries in the course of the 

 river, which in its innumerable windings through the Batoka Gorge 

 tends constantly to take this direction, but crosses by rectangular or 

 oblique traverses from one group of joints to another whenever the 

 opportunity occurs. The Chasm into which the river plunges at the 

 Falls is due to one of these lines of weakness in the rock, probably 

 a fault-plane, where a vertical belt of comparatively soft vein-stuff, 

 including a seam of crystalline calcite, breaks the continuity of the 

 harder basalt. This vein may be examined by an adventurous 

 climber in the little kloof at the eastern extremity of the Chasm ; and 

 its presence is indicated also at the inaccessible western extremity 

 by the existence of a small cave, hollowed out by the surges from t'he 

 Leaping Water. 



At the remote period when the river first began to break across 

 the eastern edge of the upland plains of basalt, the more powerful 

 action of its troubled stream in this quarter, as compared with its 

 tranquil course over the surface of the plains, must soon have 

 brought about the development of rapids, cascades, and finally of 

 a great waterfall separating the two portions according to their very 

 different working capacity. The gradual recession of this waterfall 

 by the undermining of its base and the breaking away of its edges, 

 steadily progressing throughout the long period that these conditions 

 have ruled in the Zambesi basin, are the main factors required for 

 the interpretation of all the apparently complex phenomena asso- ■ 

 ciated with the present Victoria Falls and the Batoka Gorge ; indeed, 

 it is only thus that they become explicable. Among the many 

 separate chains of evidence that strengthen this conclusion none 

 is more striking than the different manner in which the tributary 

 streams make their confluence with the main river above and below 

 the Falls. Above the Falls the tributaries have had time to grade 

 down their beds almost to the level of the Zambesi itself, so that 

 (as, for example, in the Maramba confluence) we find a back-water 

 from the main stream running for some distance into the mouth of 

 its feeder, which here occupies a scarcely perceptible valley. Below 

 the Falls, on the other hand, every tributary seems to emulate on 

 a miniature scale the example of its mighty ruler and has sunk 

 a deep gulch into the edge of the plateau roughly proportionate in. 

 length to the distance of its confluence below the Falls ; and into 

 this gulch it tumbles headlong from its older open valley on the 



