Vol. 63.~] GEOLOGY OF THE ZAMBEZI BASIN. 181 



' The regional alteration extends for some distance on either side of these 

 lines of breccia, and the indurated rocks, resisting erosion better than the 

 unaltered loose-grained sandstones, consequently form the core of the ridges, 

 hills, and mountains of this part of the country.' l 



jSTow, when the Deka Fault is plotted on the map, its prolongation, 

 so far as the present indefiniteness of the topography enables one 

 to judge, will be found to fall very nearly along the escarpment of 

 these Sijarira Quartzites as mapped by Mr. Molyneux; and I strongly 

 suspect that the lines of disturbance described in the foregoing 

 extracts represent the north-eastward continuation of the fault. 



Moreover, the phenomena are so closely analogous to those which 

 I observed in the Deka Valley, that I shall venture to suggest that 

 the ' Sijarira Series ' may be only the ' Matobola Beds ' contorted 

 and altered along this great belt of disturbance. 2 In the present 

 state of our knowledge, this suggestion must of course be merely 

 conjectural ; but it appears to fit most of the facts contained in 

 Mr. Molyneux's description of the ' Sijarira Series ' and of the 

 relations of this series to the underlying gneissose rocks and to the 

 Matobola Beds. 



If the Sijarira disturbance proves to be no other than the Deka 

 Fault, the sandstones, etc. of the Zambezi Flats on its north-western 

 or downthrow side will represent some portion of the Matobola 

 Beds of the plateau; and the steep northern face of the Sijarira Eange 

 will approximately mark the fault-scarp. This reading is, I think, 

 in accordance with our present knowledge — scanty, it is true — 

 respecting the geology of the middle reaches of the Zambezi. 



Even if the Sijarira disturbance be not the direct prolongation of 

 the Deka Fault, it must certainly belong to the same fault-system; 

 and we may recall, too, that the strike of this fault-system is 

 approximately parallel to the major axis of elevation in the ancient 

 complex farther eastward pointed out by Mr. F. P. Mennell. 3 



As regards the prolongation of the Deka Fault in the opposite 

 direction, up the Deka Valley, there is no doubt that its course was 

 marked by the range of craggy sandstone-kopjes on the southern 

 margin of the Deka basin, which we gradually approached after 

 leaving Bumbusi on our march to 'Mtoro's. 4 Farther south-west 

 this feature evidently dies away into the plain of the Kalahari, where 

 it is perhaps hopeless to expect that the fault will be traceable. 



From my examination of the fault itself at the places accessible 

 to me I could gain no evidence as to the amount — or even as to the 

 direction 5 — of downthrow, owing to its effective severance of the 



1 Quart. Journ. Geol. Soc. vol. lix (1903) pp. 279-80. 



2 On suggesting this possibility to Mr. Molyneux in the course of our 

 correspondence during the preparation of this paper, I am pleased to find 

 that he regards it as quite worthy of consideration. 



3 'The Geology of Southern Khodesia' Special Eeport No. 2, Rhodesia 

 Museum, Bulawayo, 1904, pp. 8-9 & fig. 1. 



4 See footnote on p. 178. 



5 The breadth of the crushed belt obscured the hade of the fault in the 

 sections that I examined ; but in two places — at the bend of the Deka east of the 

 Eondulu confluence (fig. 2, p. 177) and in the kopje a mile below the railway- 



