part 1] AXl) ASSOCIATED ROCKS OF MOZAMBIQUE. 71 



South of Mount Kwera a rather different type of granite 

 occurs i Jo. 28). It is pink rather than grey, and is uniform 

 and granulitic in texture. The same felspars are present, but 

 biotite is more abundant, and the chief accessories are magnetite 

 and rounded grains of zircon. Considerable quantities of the rock 

 were crushed and panned, and a heavy residue collected. From 

 this a considerable crop of zircon was obtained by the ordinary 

 methods of separation, and the mineral was afterwards analysed 

 for lead and uranium (see p. 87). A granite (Xo. 56) almost 

 identical with that of Mount Kwera occurs west of the Etipoli 

 Hills, near the Ligonia River. It differs mainly in having a 

 little muscovite in addition to biotite, and in containing less 

 magnetite. The biotites are rich in minute zircons, which are 

 surrounded by strongly-developed pleochroic haloes. Similar 

 rocks occur in the Sawa Valley (Xo. o'9), in the Xrassi Basin 

 (No. 20), and close to Ibrahimo Quartel (Xo. 18). A variety 

 much richer in biotite. some flakes of which exhibit pleochroic 

 haloes, is illustrated by an intrusion at Xatashu (Xo. 00), north- 

 west of the Etipoli Hills. The felsic mineral.- are. as before, ' 

 microcline, albite-oligoclase, and quartz, while the accessories are 

 apatite, zircon, and magnetite. A similar rock (Xo. 35) crops out 

 on the road from Fort Chinga towards Mushima. 



(3) Augite-Granites. Quaitz-Augite Diorites ; etc. 



The augite-granites, with which are associated adamellites and 

 quartz-diorites. may be described by reference to three important 

 occurrences. Two of these, in the Ampwihi and Xrassi districts, 

 are associated in the field with both crystalline limestones and 

 hornblende-gneisses ; while the third, from the slopes near Sawa 

 Cave, is associated with hornblende-gneiss alone. 



The Ampwihi specimens were collected near the road above the 

 crossing (tig. 5, p. 39). The intrusion is by no means uniform 

 throughout. The central portions are coarse-grained, and contain 

 crystals of perthitic orthoclase and slightly-rounded dark-green 

 augites embedded in a granulitic mosaic of microcline, albite- 

 oligociase, and quartz. In one specimen {Xo. 207) the proportion of 

 oligoclase is not much less than that of the potash-felspars, so that 

 the rock may be described as an augite-adamellite (Table VIII, 

 p. 72). Towards the margin in both directions the phenocrysts of 

 ovthoclase gradually die out, as a conspicuous feature of the rocks ; 

 though perthitic orthoclase is still seen, in thin sections, in larger 

 individuals than those of the surrounding minerals. At the same 

 time the augites break down into featherv a^oTeu'ates which are 

 more or less parallel, so that the rocks take on a foliated appear- 

 ance. Xear the actual contact, the texture becomes tiner, and a 

 greater proportion of the minerals have rounded aliotriomorphic 

 forms. The augites, from being crystals 2 cm. long, are reduced 

 to rounded grains 2 mm. in diameter, the total proportion of the 

 mineral being now much higher than in the interior of the intrusion. 



