434 MR. A. J. C. MOLTNEUX ON THE [Aug. I909, 



The Luano area is also constructed in the same way — a series of 

 waves and step-faults that take the Karroo beds from plateau-level 

 on the south, but differing from the mid-Zambesi basin in that it 

 shows a general lowering to the north, terminating abruptly in a 

 great fault, of 5000 feet at least, along the Machinga escarpment. 



Pre-Karroo Movements. 



The parallelism of the axes of the Karroo valleys with the 

 cleavage and folds of the contiguous schists has been already 

 mentioned. These fall into three directions : — 



(1) East-north-east. — In this lie the course of the Zambesi 

 trench from the Kafue to Feira, the Luano Valley, and several 

 ranges of hills on the Basoli plateau that are shaped by escarp- 

 ments of quartzite. 



(2) South-east. — That of the Inyanga Mountains, and the flow 

 of the Kafue, Losito, Intanga, and Lufua Rivers. 



(3) North-east. — This is followed by the cleavage and folds in 

 the Archaean rocks already noted, and is significantly the same as 

 that of the great continent-building movements of South-East Africa. 

 Mr. Lamplngh has suggested the possibility of the Deka Eault 

 causing the broken edges of the Sijarira escarpment ; while Mr. L. A. 

 Wallace has put forward the fact that the Luangwa Valley and the 

 mid-Zambesi are on the same line. I have shown that intervening 

 regions have a similar trend. 



It is thus certain that there is a zone of post-Karroo folding from 

 the source of the Deka to the head of the Luangwa — a distance of 

 over 800 miles, following the same axis of movements as those that 

 commenced in pre Karroo times. And it is this north-easterly 

 trend that influenced, first, the main plateau-axis of Rhodesia, 1 and 

 secondly, its topographical features. 



V. Physical History. 



The lowest beds of the Karroo System were laid down upon an 

 irregular surface, and it is possible that the present landscape had 

 then, so to say, been sketched out. Of the thickness which the 

 superimposed strata reached we can only estimate a minimum. In 

 Southern Rhodesia it has been given as 4700 feet — in the regions 

 now under notice it exceeded 3000 feet. 



The Karroo deposits then became involved iu tangential folding 

 operating from a southerly direction, expressed in the anticlines and 

 synclines already recorded, with some step-faulting, by which there 

 was a general northward lowering in the Luano, southward in the 

 vicinity of the Lufua, and north-westward at Sijarira. 



The amount of the downthrow caused by the Machinga Eault 



1 See F. P. Mennell, ' Geology of Southern Bhodesia ' Ehod. Mus. Report 

 (1904) No. 2. 



