part 1] AND ASSOCIATED ROCKS OF MOZAMBIQUE 7& 



on the preceding page) indicates, the rock is of the same type as 

 the Ampwihi augite-granite. In texture it is more granular, and 

 the minerals are equidimensional. Otherwise, the only difference 

 lies in the absence of peripheral amphibole around the augites 

 (Pl.X,fig.l). 



The Nrassi intrusions occur near the foot of Ericola, on the 

 western side of the hornblende-gneiss and crystalline limestone 

 exposures (see pp. 50 & 61 ; & PI. XI). The augitic rocks do not 

 form a single intrusion, but a number of sill- and dyke-like masses 

 intrusive into biotite- and hornblende-gneisses. They are them- 

 selves cut by later dykes of pegmatite and pyroxenite. The rock- 

 types represented vary from augite-granite, similar to that of the 

 Ampwihi intrusion, though coarser in grain, through adamellite 

 to quartz-diorite, by decrease in orthoclase or microcline. and quartz,, 

 and increase first in oligoclase and afterwards in andesine. Sphene,. 

 apatite, and zircon are the chief accessories, while magnetite and 

 calcite occur as in the Ampwihi rocks, and pyrite is present in 

 addition. 



(4<) Until e-bearing Uocks. 



One of the Nrassi sills, though clearly belonging to the series of 

 rocks recorded above, is remarkable for the presence of rutile and 

 pyrite and of other accessories in unusual abundance. The rock 

 ( JTo. 21) consists essentially of large crystals (2 cm. X 1 cm.) of 

 green augite and oligoclase with smaller individuals of quartz ; 

 while between these constituents occurs a granulitic mosaic of 

 quartz and orthoclase, with only a little oligoclase. Around some 

 of the augites wisps of faded biotite are seen ; but more commonly 

 there is a granulitic periphery of green hornblende, sphene, apatite, 

 and pyrite. In places the interstitial quartz-felspar mosaic is 

 associated with, or entirely replaced by, aggregates of sphene, 

 rutile, and apatite, riddled and penetrated by pyrite. In other 

 parts of the rock, veins of granular apatite and rutile with smaller 

 quantities of hornblende, sphene, and pyrite wrap round the larger 

 felspars (PI. X, fig. 3). 



The rock may be regarded as a mineralized augite-adamellite, 

 the sphene-rutile-apatite veins having been followed by pyrite.. 

 The occurrence recalls the ' krageroite ' of W. C. Brogger. 1 In 

 that rock rutile also occurs with oligoclase, and the neighbouring 

 rocks are cut by veins of apatite and rutile. 



Another Mozambique rock rich in rutile (JVb. 74), though of 

 doubtful age, may appropriately be described here. It has already 

 been mentioned on p. 47 as a vein or dyke cutting both the Monapo 

 limestone and the enclosing gneiss at the south-eastern border 

 of the former rock (fig. 6, p. 46). The rock is made up almost 

 entirely of a felt of pale-green muscovite in which occur granular 

 streaky masses, and rounded or lenticular aggregates, of vermilion- 

 coloured rutile, the contrast in colour and texture giving to the 



1 Vidensk. Selsk. Skrifter Cbristiania, Dec. 2nd, 1903. 



