298 REPORT—-1905. 
around these valleys. But even under these conditions it is not a little 
remarkable that the Matetsi basin should constitute the most conspicuous 
feature in the physiography of the basalt country, and should apparently 
be more pronounced than that of the Zambesi itself. Except in the first 
few miles below the Falls, where a shallow outer valley is traceable, the 
Batoka Gorge and its laterals trench so sharply into the plateau that one 
can rarely be aware of their position until one reaches their very brink ; 
while the Matetsi, nearly up to its head, lies within a great basin that is 
recognisable long before we reach the river. This peculiar conformation 
of the country deserves further investigation. 
It is noteworthy, as was long ago pointed out by Chapman,! that the 
course of the Deka River for a long distance very nearly coincides with 
the junction of the basalt with the sandstone. My examination of this 
junction north and west of the Wankie Coalfield showed that the sand- 
stone is locally indurated to quartzite along the line of the great fault 
that forms the boundary of the two formations, and that although in the 
portion examined the river impinges several times upon this hard belt, it 
always recoils again upon the more perishable basalts. The prolongation 
of this fault-plane north-eastward may very possibly account for the great 
northerly bend made by the Zambesi immediately below the confluence of 
the Deka. 
Geology.—The main geological features of the country have been 
already stated incidentally. The basalts, named by Molyneux the ‘ Batoka 
Basalts,’ that occupied all except about 80 square miles of the 2,000 square 
miles embraced within my traverses, represent a succession of ancient 
lava-flows that have extended far beyond the region examined. In 
their prevalent characters these basalts are remarkably uniform, con- 
sisting generally of thick bands of close-grained dark-blue rock alter- 
nating with red, purple, or ashy-looking amygdaloidal bands which mark 
off the surfaces of the separate flows. These less massive bands frequently 
show a fragmental structure and occasionally pass into fine or coarse 
agglomerates suggestive of volcanic tuffs or ashes ; but I think that this 
structure probably represents the ‘ flow breccia’ produced by the breaking 
up of the solid crust of the lava streams during the onward movement of 
their still-fluid interior. I sought for interstratified sediments among 
the basalts, but found none ; though, judging from the aspect of some of 
the railway cuttings in the Katuna valley, west of the Deka, it is not 
improbable that such may occur in parts of the plateau that I had no 
opportunity to examine, Certain thin flaggy sandstones that were 
encountered in patches on the watershed between the Deka and the 
Matetsi appeared to be newer than the basalts. Nothing was seen to 
indicate the position of the volcanic vent or vents from which the 
immense lava-flows have been poured ; and it is probable that, like similar 
‘plateau basalts’ in other parts of the world, they have had their source 
in fissure-eruptions. Their original thickness in the lower part of the 
Batoka Gorge cannot have been less than 1,000 feet, and may have been 
very much more. 
The basalts, wherever examined, were strongly jointed ; but columnar 
structure was only rudely developed and not prevalent. The main joints 
form a remarkably regular and persistent system, striking approximately 
' Travels inthe Enteriar af South Afrioa. Tondon, 1848, val. ii. p: 218, 
