Vol. 63.~] GEOLOGY OF' THE ZAMBEZI EASIX. 193 



felspars, into small round clusters (see Appendix I [F 1030] 

 p. 208). This structure was especially well seen in the bed of 

 the Matetsi River, about a mile above the railway-bridge. 



Besides the flaggy or thick-platy arrangement such as is common 

 in basalts, which was a constantly recurring character in every part 

 of the series, I noticed in a few places an unusual fissile or shaly 

 structure for which I could find no explanation. feo strongly 

 marked was this structure in the bed of the Bwani River, 6 miles 

 north of Makwa, where I first saw it, that I supposed the rock to be 

 an indurated shale or schist, until closer examination showed it to 

 possess the composition and crystalline character of the basalts. 

 This shaly-looking material was, at one spot in the Bwani, curiously 

 entangled among massive amygdaloidal basalt, with a sharp and 

 irregular junction resembling an intrusive contact. Neither in 

 the field nor under the microscope does the rock show any in- 

 dication of shearing, so that the structure can hardly be a super- 

 induced schistosity. Its petrographieal characters are described in 

 Appendix I [E 1024, 1025, & 1026] p. 209. 



This shaly structure was also conspicuous on the southern shore 

 of the Zambezi near Makwa, and was prolonged up the dry bed of 

 the Gongobujo or Logier River ; and in a less striking form it was 

 visible at a few other places, notably at the head of the Lukunguli 

 River, south-west of Dambi's. From the description given by 

 Chapman, we may gather that the basalts display a similar character 

 in the Zambezi valley for some distance below Makwa. 1 



Extent of the Basalts. 



The eastern boundary of the Batoka Basalts at the Deka Fault 

 has already been described; and I have also referred to the possibility 

 that the basic lava-flows interbedded with the ' Forest Sandstones ' 

 (Molyneux) of the country farther eastward may belong to this 

 series (p. 184). The scanty evidence respecting the northern 

 boundary as far west as the longitude of the Victoria Falls has also 

 been stated (p. 172). As to their further westward prolongation, 

 I have received information from my friend, Lieut. T. A. Gr. Budgen, 

 who accompanied us during part of our journey north of the Zambezi, 

 that he has recognized the basalts at a locality some 30 miles north- 

 west of the Falls, in the bed of the Umgwezi or Marimba River, a 

 west-flowing tributary of the Zambezi. There is, so far as I am 

 aware, no further evidence until we reach the confluence of the Chobe 



1 Chapman and Baines were evidently puzzled — and not without reason — by 

 this rock. Chapman remarks : — ' Baines thinks that the rock in the bed of the 

 Zambesi, at Wankie's, is what is called altered sandstone; it is a fissile or 

 laminated brittle rock, with a glossy coating where influenced by water, but of 

 a yellowish -brown colour inside (perhaps shale) .... The other grey scaly 

 rocks seam [? seem] in it near to Wankie's. The outer scale of this rock is 

 easily peeled off', and is brittle, but becomes harder towards the centre ' (' Travels 

 in the Interior of South Africa ' vol. ii, 1868, p. 213 ; see also p. 191). 



