414 ME. A. J. C. MOLXNETJX ON THE [Aug. 1909, 



meandering across the Karroo plain, passes completely through a 

 shoulder of the inlier by a deep cleft — evidence that the course 

 of the river was laid out at the time when the Luano was filled 

 by a mass of superimposed strata, which has since been removed by 

 erosion. 



From another inlier, Chisalisali, Kasafa is separated by a narrow 

 channel of sediments, in which the Molongushi is cutting down. 

 These show a remarkable succession of the strata, in which an 

 ascending sequence, dipping 12° to 17° northwards, of basal con- 

 glomerates, nodular ironstones, coal-measures, and fine sandy beds 

 and clays can be measured. (See PI. XXI.) 



Other 'saddles ' or domes will be noted, showing the dip of the 

 limbs in anticlines. 



If the Karroo valleys, spread out like fingers along the southern 

 fringe of the Luano, suggest a series of folds, the running brooks 

 that enter the valley through the great Machinga escarpment tell 

 of other movements. Here the contact of sediments and complex 

 follows the foot of the range in a straight line ; no Karroo beds 

 form the floors of the transverse tributary gorges on this side. 

 Each river debouches by a canon with precipitous sides, cut down 

 into the metamorphic rocks, and headed by high waterfalls where 

 the stream leaves its placid and mature course on the plateau for 

 its rejuvenated form. Thus along the line of the escarpment, in 

 addition to evidence that it was caused by post-Karroo faulting, 

 we read the message of a comparatively recent change of level in 

 the Karroo surface, by which the plateau-rivers were required to 

 fall over an emerging escarpment of Archaean rocks. It will be 

 shown later (p. 436) that this rejuvenescence and change of level 

 is due to the more rapid erosion of the sediments that probably 

 filled the Luano to plateau-level, and to the removal of some 2000 

 feet of strata. 



In describing the northern affluents of the Luano, they will be 

 taken in succession from east to west. As this valley is drained 

 eastwards, the theory of erosion would presuppose that the western 

 portion is newer and more iately removed than in the former 

 direction. 



The Lusenfwa River. — The early course of this river, the 

 only perennial one of the district, undulates across the even surface 

 of the plateau of 4000 feet, and little below its watershed contours. 

 From Boe's Ferry rapids commence, and 3 miles farther down its 

 high-level course comes to an end (3045 feet above sea-level) by 

 waterfalls of 250 feet, which head a carion of some 15 miles, cut 

 back into the plateau from the Machinga escarpment. 



The rock at the falls is a jointed gneiss, with segregations of 

 black mica, chlorite with apatite, and glassy quartz with biotite. 

 Waterworn pebbles are found high up the valley-slopes abreast of 

 this place. 



