part 1] AND ASSOCIATED ROCKS OF MOZAMBIQUE. 45 



Immediately north of Murimatigri quartz-mica-schists are again 

 found in situ, the direction of foliation, which is also that of the 

 enclosing gneisses, being now more nearly north and south. 



No. 172 is a cream-coloured to pink rock, faintly streaked with sinuous 

 shreds of pale-green biotite. Under the microscope, quartz proves to be the 

 chief mineral present, associated with felspars which have suffered extreme 

 granulation. The quartzes, too, are generally granulated around the periphery, 

 and the unbroken cores show evidence of straining by their undulose extinctions. 

 Small granules of epidote, garnet, and apatite, generally enclosed within the- 

 biotite-shreds, are also present. (See PI. VIII, fig. 3.) 



No. 171 was found near Ibrahimo, where the schists or granulites are 

 cut in places by coarsely-felspathic tourmaline-bearing pegmatites. It is 

 a glassy -looking quartz -granulite, spangled with parallel flakes of muscovite. 

 I n thin section, the rock is seen to be completely recrystallized to a coarse- 

 mos -:aic of quartz, penetrated by lath-shaped crystals (seen in one direction as 

 elon gated plates) of muscovite, which are remarkably straight and paralleL 

 Apa +^e and small crystals of toiirmaline are also present as inclusions. 



The rocks described above are clearly of detrital origin, and the 

 fact that they exhibit unequal degrees of metamorphism is perhaps- 

 due to the circumstance that the region has suffered at least three 

 periods- of intimate penetration by granitic magmas. It is of even 

 greater interest that they represent a differentiated series of de- 

 posits, including argillaceous, felspathic, micaceous, and ferruginous: 

 sandstones. These formations, laid down before the gneisses were 

 intruded, indicate that in those early times denudation and deposi- 

 tion had already begun the regular course that is revealed to us by 

 the records of the later formations. Moreover, not only were the 

 processes similar, but the rocks which suffered decay by their 

 activities — rocks of which only a few clastic grains now remain — 

 must also have been closely akin to those exposed in Mozambique 

 to-day ; that is, they were of granitic composition. 



j^jo. 1 76. In the Mukumburi Valley, due west of Memba, a 

 dark-green hornblende-schist containing irregular bands of quartz 

 and felspar is found interfoliated with the gneisses. 



In thin section (PI. VIII, fig. 4) it is seen that hornblende predominates 

 along certain bands, while between the latter occur lenticular areas in 

 which the chief constituents are, in some cases, distorted quartz, in 

 others quartz and felspar, and sometimes felspar without quartz. The 

 felspar is usually oligoclase, but some orthoclase is also present, and both 

 types are conspicuously elongated in the direction of foliation. Between 

 the dark and Light bands, granular clusters of epidote, and occasionally 

 of sphene, are present; and these minerals, especially epidote, are also 

 arranged in sinuous lines throughout the rock, but more particularly among 

 the felspars. Minute apatites are included in hornblende and felspar, 

 and both quartz and felspar contain blebs of calcite, which does not seem to 

 owe its origin to weathering processes. 



This rock may be of composite origin, due to the interaction of a 

 granite magma with a dolomitic limestone; but, on the other hand, 

 the mineral composition is precisely what one would expect to 

 arise from the metamorphism of a basalt or dolerite. Augite 

 would yield hornblende and quartz, leaving over a little lime ; this. 



