Vol. 63.] GEOLOGY OF THE ZAMBEZI BASIN. 203 



found issuing from the fault-rock low down in the eastern recess 

 of The Chasm at the Victoria Falls. The temperature of this 

 anomalous little fountain indicated that it was fed from the river 

 above ; and although within the perpetually spray-drenched atmo- 

 sphere of The Chasm, it had deposited a thick cushion of tufa, 

 charmingly overgrown with moss and fern. 



Traces of a calcareous layer underlying the alluvial loam were 

 noticed, in places, on the flats bordering both sides of the Zambezi 

 above the Falls. It will be remembered that Livingstone found 

 thick calcareous deposits in a higher part of the valley, and believed 

 them to be the relics of a lake which was drained by the opening 

 of the rift at the Palls. 1 



Besides the ' valley-calcretes,' I saw in a few places somewhat 

 similar deposits of greater antiquity, that could not have been 

 formed under existing conditions. These were generally associated 

 with chalcedonic quartzite and with hard ferruginous material 

 (' ferricrete '), which appeared in part to replace them and to 

 represent a gradual alteration that is probably still in progress. 

 Dr. Passarge has dealt very fully with the alteration (verkiesel- 

 ung) of lime-rocks into quartzites in the Kalahari; and I think 

 that this process must have taken place in the cases to which I 

 refer. 



My best opportunity for examining material of this kind was 

 near our camp at Makwa, just after we had crossed the Zambezi. 

 Here the river, having emerged from the Batoka Gorge, has again 

 expanded into a wide shallow stream, bordered by an irregular flat 

 diversified with steep-sided basaltic kopjes of varying height. Two 

 of these kopjes that I examined are capped by the deposits in 

 question ; and I should probably have found the same conditions 

 on other hills in the neighbourhood, if I had been able to reach 

 them. The first kopje overlooks the right bank of the river close 

 to our landing-place, and is the ' Logier Hill ' of Chapman and 

 Baines, described by the former as being composed of 4 tufa, 

 dipping eastward.' 2 On this hill I estimated the thickness of the 

 superficial rock at about 20 feet, the material being partly siliceous 

 and partly calcareous, but showing the same rugged cellular 

 structure throughout the mass. A similar but thinner capping was 

 observed on the second kopje, near our camp 1^ miles west-north- 

 west of Logier Hill, which rose to about the same elevation and 

 stood in like position with regard to the river. These hills are both 

 much below the general level of the plateau, and must have received 



1 ' Missionary Travels & Researches in South Africa ' 1857, chap, xxvi, p. 527. 



2 ' Travels in the Interior of South Africa ' vol. ii (1868) p. 213. I was 

 anxious to determine this site, so famous in the annals of African travel, 

 where Baines and Chapman in 1862 made their unsuccessful attempt to build 

 a boat in which to pass down the Zambezi. My ever-helpful pilot for the 

 southern traverses, the late H. F. Greer, the Assistant Native Commissioner for 

 the district, therefore called in some of the oldest natives to guide us to the 

 place; and there, on the very spot, two of them told us how, as boys, they 

 had come across the river to see the first white men in their country, — 

 Grabimani (as they called Chapman) and his comrades — giving us a faithful 

 narrative of the doings of these impressive strangers. 



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