7(5 DE. A. HOLMES ON THE PRE-CAMBKIAISr [vol. lxXlV,. 



VII. The Geaisttes and Massive Pegmatites. 



The latest granitic rocks of Mozambique consist mainly of 

 massive pegmatites, but occasionally small intrusions of granite 

 are exposed, in which the minerals are more uniformly distributed, 

 and the grain is less coarse, than in the pegmatites. The chief" 

 rock- types may be classified as follows : — 



Granites. 



Biotite-granites. 



Muse o rite -granite s . 

 Pegmatites. 



Graphic granite. 



Coarse quartz -felspar pegmatites. 



Pegmatites with hasmatite. 



Pegmatites with magnetite. 



Pegmatites with ilmenite. 



Pegmatites with sulphide minerals. 

 Tourmalinized rocks. 



(1) Biotite- and Muscovite-Granites. 



Between Mitikiti and the Monapo River there was found during 

 a journey eastwards from Nambako, a broad dyke-like mass of red 

 biotite-granite (JVo. 6). This rock consists of red perthitic ortho- 

 clase with interstitial smoky quartz, and in places small flakes 

 of biotite. In thin section it is seen that isomorphic crystals 

 of oligoclase are present in small amount, wrapped round by 

 the orthoclase. The biotite contains numerous pleochroic haloes 

 around zircon inclusions, and a little muscovite is also present. 

 The accessory minerals are apatite and zircon, with very little 

 magnetite. 



In the same neighbourhood occur numerous dykes and sheets 

 of massive red felspathic pegmatite, with pockets of quartz and 

 small sheaves of biotite. The detailed similarity between these 

 minerals and those of the granite suggests a genetic connexion 

 between the two groups of rocks. 



A similar granite (JVo. 3), but with flesh-coloured phenocrvsts 

 of orthoclase (recalling the Shap Granite in its megascopic aspect), 

 was found among the rock-debris occurring along the shore of 

 Mosuril Bay near Ampense. 



Near Fort Ligonia (Zambesia), on the south side of the Ligonia 

 River, the complex of gneiss and granulitic granite is cut by 

 numerous sheets, 2 or 3 feet thick, of muscovite-granite. The 

 minerals {No. 159) are quartz, orthoclase (not perthitic, but in- 

 cluding small hypidiomorphic crystals of oligoclase), and abundant 

 muscovite. Accessories are rare, and only magnetite and zircon 

 have been seen. The late R. L. Reid also recorded muscovite- 

 granites and pegmatites from the neighbourhood of the Monapo- 

 Limestone. 



