178 MR. G. W. LAMPLTJGH ON THE [May I907, 



sandstone and basalts which I had previously noticed at 'Mtoro's 

 Kraal, 8 or 10 miles west-south-west from the Deka railway-crossing, 

 lay approximately upon the opposite continuation of the same fault- 

 line, although I had at the time thought it of slight consequence. 



My personal knowledge of the faulted belt thus embraces a 

 distance along its direction of 16 or 18 miles ; but there is evidence 

 that it is much farther prolonged in both directions, and is a 

 structural feature of prime importance in the geology of the region. 1 

 The phenomena associated with it are also of sufficient interest to 

 deserve particular description. 



In the segment that came under my observation, the strike of 

 the fault is from west-south-west to east-north-east. For a long 

 distance its course coincides very closely with that of the Deka 

 valley : not, however, that the valley is a fault-trough, but because 

 of a secondary effect presently to be discussed. It was long ago 

 observed by Chapman, whose testimony should in itself have led 

 one .to suspect the faulting, that — 



• ' The Luluesie or Daka Kiver is the limit of the basaltic rocks, presenting 

 formidable cliffs of red sandstone, while the western banks have at intervals 

 mural cliffs of basalt, and thus throughout the whole distance which I traversed 

 (upward of 80 miles), I have seen no red sandstone west of the Luluesie, nor 

 basalt east of it, excepting only in the banks where the river, by an abrupt 

 bend, has encroached on either side a little.' 2 



Some details of the fault at the places where I had the best 

 opportunity for examining it, north and west of Wankie, are shown 

 in the plan (fig. 2, p. 177) and diagrammatic sketch (fig. 3), and in 

 Section 3 of PL XVII. Its course and probable prolongation are 

 represented on the map ; but in this I have been greatly hampered 

 by the uncertainty of the topography, especially with respect to the 

 position of the localities in the upper part of the Deka basin, between 

 Deka and 'JNgoni's Kraal, which may be several miles from their 

 true bearings on the fixed position of Wankie. 



The fault affects in a striking manner the sandstones which abut 

 upon it. In all the places that I examined, except in the transverse 

 valley of the Eondulu Eiver, these sandstones are of the red coarse- 

 grained or pebbly type, and appear to belong to the ' Upper Grits ' 

 of the Wankie Measures, as indicated in Section 3 (PL XVII). In 

 some places (fig. 3, p. 177) these sandstones plunge steeply as they 

 approach the fault, and are not only greatly crushed and contorted, 

 but are also converted into quartzite and much veined with quartz 

 and haematite, thus producing a highly indurated belt bordering the 

 dislocation. 



The basalts are also affected, but in an opposite manner, the 

 altered rock along the fault yielding more readily to the weather 



1 Since the above was written I have received a letter from my friend Mr. 

 Kearney, in which he informs me that he has recently traced the fault south- 

 westward for 30 miles, from Wankie to Bumbusi, and finds its course to be 

 parallel with the road that I followed and sometimes within a few hundred yards 

 of it, as I had suspected (see p. 181;. 



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



