104 SECTIONAL ADDRESSES 
weather sequence throughout the year; and the second concerns the. 
regimen of rivers. I would draw particular attention to this matter, so 
important for the population ; we have received a statement from every 
District as to the permanence of streams and their flood character. 
PuysicaL ENVIRONMENT. 
In order to have space for matter that is now available for the first time, 
I will describe the physical background in barest outline, mentioning only 
such facts as are important to the understanding of the human geography. 
The fundamental crystalline skeleton of Africa appears here in two 
broad zones extending respectively from S.W. to N.E., occupying the 
south-eastern belt, and S.E. to N.W., extending over into the Katanga. 
The structure of this latter zone is complicated by the presence of a 
geosyncline of ancient continental sediments, including dolomitic lime- 
stones, that were folded by thrusts from the S.W. ‘Their outcrops, 
therefore, lie along an are concave in this direction. Associated with 
these folds and with certain igneous intrusions is the mineralisation of 
the zone, by lead and zinc in Broken Hill and by copper and other ores 
farther north. The south-eastern zone is seamed by a structural depres- 
sion in which sediments of ‘ Karoo’ age are preserved, said to contain 
coal as well as nitrates sporadically quarried by the natives for gunpowder. 
The Luapula basin in the north is largely underlain by Palzozoic sedi- 
ments, but with granite intrusions, while throughout the drainage area of 
the upper Zambezi the ancient rocks are almost completely masked by 
the Kalahari sands. 
The relief of Northern Rhodesia, like that of most of the Central 
African highlands, is monotonous. Planation over long periods accounts 
for this ; and consequently the hill ranges and inselbergs which form the 
chief accidents on a plateau standing mostly between 1,000 and 1,500 m. 
are chiefly residuals of stronger rock, while the more extensive elevations 
above this height, notably those dividing the Bangweolo ‘ saucer’ from 
Tanganyika and from the Luangwa valley, will probably be explained 
by warping. The entire plateau seems to bear traces of indeterminate 
drainage with numerous evidences of river capture on all scales and of 
varied date. By far the most pronounced relief features are the margins of 
the south-eastern structural furrow drained convergently by the Luangwa 
and the Zambezi below the Batoka gorge. This, both on account of the 
height of the escarpments—generally more than 400 metres—which are 
to be regarded as erosional fault-scarps, as well as because of their extreme 
dissection by the regressive erosion of tributaries which are rapidly 
notching the plateau rims on both sides. 
Time does not permit me to deal statistically with the climate, which is, 
of course, of inter-tropical type with markedly seasonal rainfall. In 
Rhodesia three seasons are recognised and named by the natives, the 
limiting dates varying with the locality: the cool season from March, 
April or May to July or August ; the hot, dry season from July or August 
to October or November ; and the rainy season lasting from these months 
to March or April. But in some districts, where there is a temporary 
break in the rains of from one to three weeks in December to January, a 
