Yol. 59.] SEDIMENTARY DEPOSITS OF SOUTHERN RHODESIA. 279 



eastern districts a thickness of 1600 feet of horizontal strata is un- 

 represented : these, if ever deposited, have been subject to erosion. 



The difference of altitude between the Zambesi River and Thaba 

 'Sinduna is 3500 feet, which, allowing- for the dip of the beds in the 

 Sengwe Coalfield, and for further strata below Zambesi-level, must 

 give a minimum thickness to the sedimentary deposits of .Southern 

 Rhodesia of 4700 feet. 



The largest area in which the beds have been tilted is that around 

 the Sijarira Range, and it is along a line following a north-easterly 

 direction. While the summits of the range show some curved or 

 folded strata, it is noteworthy that the rocks at the base of the 

 range on the north side are unaltered and horizontal — thus 

 proving the crumpling to be merely local. On the north-east the 

 elevatory movement died out, and on the south-west the dip veers 

 round to that direction. 



Along the Sengwe Coalfield, the parallel direction of the escarp- 

 ment, the plains, and the Sijarira Range is very noticeable, and 

 this is owing to the tilting of the beds by which the softer coal- 

 bearing strata have been exposed to more rapid decay. At present 

 the Matobola Plains, which run along the strike of the coal- 

 bearing beds, occupy a trough between the escarpment and the up- 

 tilted edges of the lower group of sandstones ; and this depression 

 continues for over 100 miles across this portion of the country. By 

 the quicker decay of these beds, and the consequent trough-like 

 valley thus formed, the rivers draining this area have had to force 

 their way through narrow gorges in the Sijarira Range and the 

 mountains lying between the plains and the Zambesi. The gorge of 

 the Lubu has already been referred to. The Sengwe, which rises 

 on the high plateau to the south, and descends to the Matobola 

 Plains, is joined by many rivers that drain these flats, and also 

 runs through the range of hills to the north by a deep and narrow 

 gorge. Farther east again are the Sesami River and the Bume (or 

 Omay), which also cut their way through the hills from the flat 

 country drained by them. 



Where the quartzites or indurated rocks occur, it may often be 

 noticed that there is a fault-fissure or displacement, and the axes 

 of these movements take a north-easterly direction, or at right 

 angles to the dip. 



Thus at Chongolo the rocks are indurated on either side of a dyke 

 of shale-and-sandstone crush-breccia. At the Lubu are parallel 

 dykes of crush-breccia, made up of angular blocks of red sandstone, 

 cemented by secondary white silica ; and at many other localities 

 it is noticeable that movements have taken place along lines 

 following a north-easterly direction, and have crushed the rocks 

 into angular fragments, now cemented together. 



In no place have I yet seen two beds of different characteristics 

 brought into proximity by these larger earth-movements, and the 

 vertical displacement of the strata cannot be ascertained. The 

 thickness of the few varieties of coarser sediments is so great that 

 the dislocation might be immense without bringing rocks of different 



