Vol. 65.] THE KARROO SYSTEM IN NORTHERN RHODESIA. 411 



probably Karroo age. In the vicinity of the Lusenfwa junction, 

 hills of gneiss close in on the river ; but afterwards the walls 

 recede at greater slopes, and the work of subaerial denudation is 

 much more marked. Down to this bend the direction of the 

 valley has been parallel with the strike of the schists. 



The Lukasashi Valley. 



This is another notable feature : the Lukasashi Eiver running 

 parallel with the Luangwa and the strike of the schists, and in a 

 similar trench-valley at the back of the Machinga escarpment. It 

 rises near Serenje on the plateau, but for the lower 90 miles its 

 valley has a floor of Karroo beds. On nearing the junction with 

 the Lusenfwa, it bends and cuts across the cleavage of the schists. 

 Notes and sections on this locality, for which I am indebted to 

 Mr. J. M. Moubray, show that the valley below this bend intersects 

 four small transverse valleys of sediments, divided by Archaean 

 ridges, and apparently resembling the synclinal folds of Karroo 

 strata (with axes corresponding to the strike of the Archaean 

 rocks) which occur in the Luano Valley (p. 413). 



All the following localities will be described from my own 

 observations, and I have, in them, been fortunate in having 

 had the opportunity for more detailed study of their physical 

 conditions than is generally the case when traversing wide 

 areas : in this way I have gathered facts which are of more than 

 merely local value, and bear significantly on the history of all these 

 troughs and escarpments and their associated physiography. 



The Luano Valley. 



This is a wedge-shaped depression, the base of which lies upon 

 the Lukasashi, while the apex rests 28 miles away from the railway 

 from Victoria Falls to Broken Hill (see fig. 2, p. 112). Its length 

 is upwards of 80 miles, and the width reaches 25 miles. The walls 

 are represented by the plateau-ramparts, which thus draw together 

 on the west. 



The northern wall, here also known as the Machinga, is wonderful 

 for its uniform sky-line, and emphasizes the flatness of the northern 

 Khodesian plateau, as shown in fig. 1 (p. 410). It maintains a general 

 direction to the east-north-east, and is lost in the haze of the 

 distance. The echelon of bluff's shows it to be cut back in ravines 

 where the smaller mountain-torrents are at work, and incised by 

 deep gorges where important rivers have eroded courses from 

 mature plateau-level to the plain. These rivers unite with the 

 Lusenfwa as the main channel of drainage. The term Luano is 

 regional for this low area, and is derived from the Aluano people 

 who inhabit it. The escarpment is formed of gneiss and schist 

 which dip southwards, and in this closely correspond with the 

 angle of slope of the foothills. In consequence, subaerial erosion 

 is vigorous, and vast blocks of rock constantly fall away, scouring 



