part 1J AND ASSOCIATED ROCKS or MOZAMBIQUE. 35 



.rapidly cooling after sunset, frequently split with a loud report. 1 .. 

 Id the Ribawe Mountains, where the base-camp of the Memba 

 Minerals Expedition was situated in 1911 (surrounded on three 

 .sides by high peaks rising 2000 feet above the valley), the report 

 of a splitting rock and the noise of its fall was noticed during the 

 night on several occasions. 



Where the peaks lack a simple outline, and are capped by 

 irregular knobs, the latter can generally be explained as an addi- 

 tional breaking-away of the rocks along foliation-planes, and along 

 joint-planes inclined to them. A peak in the Kobe Hills, near 

 Memba, provides an admirable illustration (figs. 2 & 3, p. 36). Seen 

 from the south the summit is smoothly rounded, the convex sides 

 dropping steeply to the plain below and truncating the banding 

 of the gneiss, which is here nearly horizontal. From the east, 

 however, the profile is very different, and shows an overhanging 

 rectangular block that has been formed by fracture along joint- 

 planes. 



The plateau-surface rises almost uniformly until it culminates in 

 the Xamuli district. 300 miles from the Indian Ocean, at a height 

 of 3000 feet. Similarly, the inselberge and mountain-blocks 

 steadily increase in altitude towards the west. Within 50 miles of 

 the sea few of the peaks attain 1000 feet. West of Xampula the 

 Mwipwi Mountains and the Xamahuga Range approach 3000 feet 

 above sea-level, or 2000 feet above the plateau. The Chica Kange 

 reaches 4000 feet, the highest of the Ribawe peaks 5000 feet, 

 while many of the peaks of the Mrupi, Mluli, and Mripa moun- 

 tains exceed that figure. The highest summit of Inago rises to 

 0190 feet, and that of Xamuli, the highest peak in Portuguese 

 East Africa, to 8050 feet. 5000 feet above the broad and fertile 

 valley of the Malema. 



The river-systems are closely related to the structural directions 

 of the country, nearly all the streams and the watersheds between 

 them being either parallel or perpendicular to the foliation direc- 

 tions of the gneissose granites. 2 The basins of the Mukumburi, 

 the Monapo, and the Mluli Rivers fall entirely within Mozambique, 

 and the rest of the territory is watered lyy the border rivers, the 

 Lurio and Livonia, and bv their tributaries from the south and 

 north respectively. All the larger rivers and their important 

 tributaries, except the Monapo, rise in the high mountain-groups 

 of the interior. The upper courses are fed continuously through- 

 out the year ; but the middle and lower tracts become wide and 

 shallow, and, except for a few stagnant pools, they dry up during 

 several months of the year. Recent rejuvenation is indicated by 

 "the gullies cut through thick deposits of sand and gravel, and 

 bv small hansrino; valleys which are sometimes seen anions: the 

 mountains. A corresponding uplift is demonstrated along the 

 coast by the existence of raised beaches and coral-reefs. 



1 ' Expedition to the Zambesi, &c.' p. 492. 



2 See A. Holmes & D. A. Wray, Geogr. Jovrn. vol. xlli (1913) map on 

 p. 145. 



d2 



