part 1] AXD ASSOCIATED EOCKS OF MOZAMBIQUE. 55 



Augen-gneisses of the ordinary type are rare, the more common 

 transition from coarsely-banded gneisses towards granites being 

 through a series of types that may be described as glomero- 

 plasmatic. In these rocks numerous clusters of small biotite - 

 flakes are distributed through a granular mass of quartz and 

 felspar. The biotite assemblages are generally so drawn out that 

 the rocks have an irregular foliation. It is as though the darker 

 streaks of the banded gneisses were broken up and distributed 

 more evenly through the rock, the individual biotites still retaining 

 a semblance of directive structure. By the loss of this structure, 

 the rocks gradually pass into granulitic granites. Should por- 

 phyrinic crystals of orthoclase be present, their alignment indicates- 

 the direction of flow, but otherwise the granites are almost devoid 

 of the directive structures displayed by the gneisses. 



No. 38 a, from the eastern slope of the Etipoli Hills, facing the Lalaua 

 River, is a characteristic example of the glomeroplasmatic gneiss. It is 

 noticeably less granulitic than the gneisses already described, and there 

 are even patches in which the felspars (microcline) are idiomorphic. The 

 biotite, like that of the Ligonia augen- gneiss, is a sage-green variety. 

 and with it are associated hornblende of a darker green, greenish -brown 

 sphene, and apatite. Qnartz and oligoclase are also found near the biotite 

 aggregates, while away from them the rock is almost exclusively composed 

 of quartz and microcline, with occasionally a small flake of biotite. In the 

 leucocratic parts of the rock rounded zircons are present as inclusions. 



Similar rocks, but without hornblende, are found on the northern slopes of 

 Mhala (No. 38b), the middle member of the three peaks that constitute the 

 Etipoli Hills ; and they also occur on the southern slopes of those Hills, and 

 on the south-western slope towards the Ligonia (No. 70). The same type of 

 gneiss has also been found on the slopes of the Mwipwi Mountains, north- 

 west of the Namieta Eiver, and on the sides of Palalani Hill in tne same 

 neighbourhood. 



No. 46 is an almost identical rock (somewhat richer in microcline) from 

 another hill called Mhala, south of Nakavala's Kraal, near the source of the 

 Ampwihi Eiver. In'the district north-east of the Eibawe Mountains the same 

 rock-type was found in the Namosa and Ericola Hills, and on the southern 

 slopes of the Muima Eange. 



To sum up, the glomeroplasmatic gneisses have been found 

 only on the slopes of the hills and inselberge peaks. Towards the 

 adjoining valleys or plains they merge outwards into banded 

 gneisses that usually are conspicuously richer in biotite ; while in 

 the hills themselves, especially in the case of the larger mountain 

 groups, they pass inwards into granites much poorer in biotite. 

 These rocks will nov\ T be described. 



No. 52 was collected from the upper slopes of -Mhala (Etipoli Hills), where 

 it occurs above the glomeroplasmatic gneiss 38 b. It is a granulitic rock, 

 pink to cream in colour, with occasional dark irregular patches containing 

 flakes of biotite. Under the microscope these are seen to be of the same 

 green as the flakes in 38 a and 38 b ; but there is no alignment, and even 

 the quartz -microcline mosaic that makes up the rest of the rock is devoid 

 of any directive structure. The mineralogical composition is recorded in 

 Table V (p. 53), and it shows in relation to the associated gneiss a marked 

 deficiency in biotite and oligoclase. The accessories are mainly apatite 

 and zircon, and a point of interest is that the biotites contain exceedingly 

 dense pleochroic haloes. 



