Extension of tJte Karroo Lavas. 167 



During the last two years the writer has made a number of journeys 

 through Northern Ehodesia and Portuguese East Africa, one of the 

 results of which has been to show that the lavas of this period have 

 an extension considerably further northward and eastward than ha^ 

 been generally recognized. This is not to say that the volcanic 

 rocks themselves have escaped notice — though even this appears to 

 be the case with the first area to be dealt with — but their age has 

 not been determined. Hence a few notes on the occurrences may not 

 be out of place, though these are necessarily brief, as constant 

 travelling has prevented any detailed petrographical investigation 

 of the features the rocks present. 



Northern Area. 



From the railway bridge crossing the Kafue River in Northern 

 Rhodesia, some 250 miles north of the Zambesi bridge at the Victoria 

 Falls, there can be seen almost due east some hills in which the 

 discerning eye Mali detect distinct indications of a synclinal structure. 

 The only doubts arising as to the reality of this arrangement are due 

 to the fact that the whole area round about is one of Archaean rocks. 

 However, a journey of about 10 miles across the Kafue Flats enables 

 this point to be settled, and the stratified arrangement of the rocks 

 becomes clearer as the hills are approached. It is probable, indeed, 

 that a strip of sedunents really underlies the alluvium of the flats 

 almost up the bridge itself, but it is not till in the immediate 

 neighbourhood of the hills that any unmistakeable signs of them are 

 seen, in the shape of a few feet of soft reddish sandstone in the bank 

 of a small stream. It may at once be said, however, that the hills 

 themselves, which ate 600 or 700 feet high, are entirely volcanic, 

 and the well-marked step-like appearance they present when seen 

 from the south indicates that they consist of six or seven distinct 

 flows, the number adopted depending on whether the faintly marked 

 ridge stretching out from beneath the last of the much steeper scarp« 

 above is basalt or the top of the sandstone, a point which- had to 

 be left undecided. Water-level in the Kafue is about 3,200 feet 

 above the sea, so that the tops of the hills must reach to nearly 

 4,000 feet, the western edge already referred to not being quite the 

 highest point. 



An examination of the area showed that the lavas, etc., extend for 

 10 miles or more east of their first conspicuous outcrops, and probably 

 form a complete basin elongated in that direction. Both north and 

 south they are flanked by much more irregular slopes of the ancient 

 gneisses and schists which emerge from beneath them. Whethfet 

 there is any faulting round the margins of the younger rocks canri6t 

 be defijiitely decided in the absence of any clear sections 6f ' W.Q 

 junction, but though suspicions were entertained that such might' %te 

 the case, the conclusion was eventually reached, after closfe 

 investigation, that the base of the sediments rested directly upon'thte 

 ancient schists and gneisses. These sediments consist of sandstones 



