68 THE PRE-CAMBRIAN ROCKS OF MOZAMBIQUE. [vol. lxxiv. 



generally be easily determined from the fact that the} r cut across 

 the gneissic foliation, and often contain inclusions of the associated 

 gneiss. Fig. 7 (p. 67) is a drawing of a granulitic granite-intrusion 

 exposed on a vertical face of the western slope of Mhala, Nakavala. 

 The entire hill is riddled with innumerable tongues and apophyses, 

 sometimes parallel to the foliation, but often cutting across 

 obliquely or at right angles. Only on the lower slopes is it possible 

 to find greater masses of granite from which the long irregular arms 

 have sprung, and even these greater masses are rarely more than a 

 few feet across. In many places thin aplitic veins have been 

 injected in lit-par-lit fashion along the foliation-planes, converting 

 the rock into a banded composite gneiss. In other places, the 

 tongues and apophyses thread the older rocks so abundantly that 

 the foliation is extremely contorted, or becomes so confused that it 

 almost ceases to exist. 



Farther west the intrusions become larger and more continuous. 

 The augite-granite above the Arnpwihi crossing (figs. 4 & 5, pp. 38- 

 39) is a good example, and will be described below. North of the 

 Elba we Mountains, the Karji and Koldwi Hills are largely made 

 up of an intrusive granulitic granite, though numerous inclusions 

 of gneiss still remain. In the Bibawe Mountains themselves, 

 occurs a biotite-granite with porphyritic crystals of perthitic 

 orthoclase, and similar intrusions were noted in many of the 

 hills surrounding the Nrassi basin. In the plains of the Nrassi, the 

 granite is generally found in sill-like masses rarely exceeding 2 or 

 3 feet in thickness, or as larger intrusions having a laccolithic 

 form. 



It is a noteworthy fact that the smaller intrusions are nearly 

 always free from biotite, although many of them carry small 

 crystals of haematite. The larger intrusions have generally a small 

 proportion of biotite, while those that have traversed hornblende- 

 gneiss, or have come into contact with crystalline limestone, are 

 characterized by the presence of augite as the chief coloured 

 mineral. 



(1) Pegmatites. 



Pegmatites are frequently associated with the granulitic granites, 

 from which they are distinguished by the tendency of minerals of 

 the same kind to group themselves together in irregularly-shaped 

 masses. Quartz, occupying the interior of the mass, is generally 

 coarsely granulitic in texture, and felspar less so ; while, if biotite 

 be present, it occurs in pockets carrying large strongly-cleaved 

 individuals, either enclosed within the felspar or arranged around 

 the periphery of the intrusion, especially in the neighbourhood of 

 angular terminations (see figs. 8 & 9, p. 69). Between the central 

 quartz aggregates and the surrounding orthoclase, there is frequently 

 a narrow granulitic zone composed of quartz and orthoclase in 

 about the same proportions as in graphic granite. In other cases, 

 a similar zone containing flakes of biotite arranged in haphazard 

 fashion, surrounds the felspar (fig. 10, p. 69). 



