206 R. R. Walls— The Geology of Portuguese Nyasaland. 



similarities iii the field with the rocks of the Swaziland system ia 

 the Transvaal, and as they are absolutely devoid of fossils and appear 

 to lie on a crystalline complex of granite and gneisses it is probable 

 that they belong to the very oldest Palaeozoic rocks. As in the 

 Swaziland system, bedded iron ores are very common. At one 

 point, nearly 150 miles from the mouth of the Lurio, the quartzites 

 form steep escarpments, and the iron ores are Avell exposed. As- 

 the rock weathers the heavier iron ores accumulate below, while the 

 lighter materials are washed away in the rainy season. The natives 

 gather the ore by hand and smelt it with wood charcoal. They 

 show remarkable ingenuity in fashioning spear-heads and axes in 

 this crude manner, though the iron is naturally very soft and not 

 of much value. 



Throughout the gneisses of the interior and the quartzites of the 

 Lurio valley intrusive granite is very prolific. The granite always 

 appears of much- later date than the intruded rock, and yet often 

 ramifies through the gneisses and quartzites in such a fashion as to 

 suggest that ih.Q granite itself has been subjected to subsequent 

 folding with the country rock. A good instance is seen in the granite 

 intrusion immediately to the west of the Tertiary deposits in the 

 immediate neighbourhood of Pemba Bay. Seams of v;hite quartz 

 are prolific over all the metamorjihic rocks of the interior, and are 

 rather a conspicuous feature. Seams less than 2 inches- thick 

 can often be traced for many hundreds of yards, piercing gneiss, 

 schist, and quartzites alike in wavy lines, quite independent of the 

 bedding or folding. 



The rock outcrops of this country deserve particular note. The 

 Tertiary deposits of the coast have been thrown up to form raised 

 beaches generally marked ofi sharply by fault-lines. These Tertiary 

 deposits retain their horizontal bedding to a marked extent, and 

 are free from folding and contortion although faulted. The out- 

 crops of the older rock of the interior are very distinct however. 

 They are typical Inselberge or isolated mountains, though of 

 different architecture. They may rise to a height of 500 feet or more 

 above the general level or they may appear a few inches only above 

 the soil in the bush. (See PI. VIII.) They may be differentiated 

 into : {a) Bosses of granite evidently intrusive and irregular in plan ; 

 (6) steep anticlines of folded metamorjjhic rock and gneiss oval in 

 plan ; (c) escarpments of metamorphic rocks and quartzites generally 

 more elongated than the latter type. These three types have 

 remarkably smooth surfaces, so smooth, in fact, that it is very 

 unusual to find any soil or plants other than the most minute species 

 growing upon them. The other type {d) of Inselberg is sharply dis- 

 tinct from the three foregoing types, and is composed of huge broken 

 and contorted boulders lying promiscuously one on the top of the 

 other. This latter mountain is typical of regions where intense 

 contortion and crushing of the rocks have taken place by folding 

 in two or more different directions. For example, it is found in 



