part 1] AJND ASSOCIATED KOCKS OF MOZAMBIQUE- 61 



The authors also tabulate a series of analyses (Joe. cit.) illus- 

 trating the transition, and these show a regular decrease in potasli 

 as the limestone is approached, while soda first increases and 

 afterwards decreases even more rapidly than the potash. In a 

 later study of the region. W. G. Fove l correlates the liberation 

 of alkaline solutions by amphibolitization with the production of 

 nepheline-syenites. 



The hornblende-gneisses and amphibolites on the eastern side of 

 the Ampwihi limestone are similar to those now described, except 

 in the general absence of garnet from the specimens collected. 



In none of the other localities where hornblende-gneiss and 

 amphibolite were found was it possible to trace the transition from 

 biotite-gneiss on the one hand, or towards crystalline limestone on 

 the other, as completely as in the Ampwihi district. 



Hornblende-gneiss occurs in the bed of the Nrassi River near 

 the camp south of Ndrapo, associated on both sides with biotite- 

 gneisses that have been thickly threaded by later pegmatites. 



The rock (No. 20) is dark and heavy (S.G. — 3'07), and is slightly foliated 

 owing to the elongation of the hornblende individuals and the arrangement of 

 both white and coloured minerals in sub-parallel drawn-out aggregates. The 

 hornblende is a dark greenish-brown strongly-pleochroic variety, in places, 

 however, becoming nearly colourless. It is slightly more abundant than the 

 felsic minerals, which are beautifully fresh, and consist of labradorite and 

 quartz in the proportion of about two to one. The accompanying accessories 

 are (in order of abundance) sphene, apatite, and zircon. 



A similar rock {-No. 58), but exhibiting less foliation and con- 

 taining a little biotite in addition to hornblende, occurs in associa- 

 tion with crystalline limestone (JSTo. 93, p. 50) in a gully that 

 carries part of the Ericola drainage to the Xrassi. Towards the 

 limestone, the gneiss loses its distinctive foliation, and becomes 

 a thoroughly massive amphibolite (Xo. 59) free from biotite. 



On the steep slopes near the Sawa caves (east of Sawa base-camp), 

 a coarsely foliated hornblende : gneiss (A 7 ©. 48) occurs, cut by later 

 sill-like intrusions of augite-granite. The minerals present are the 

 same as in the Xrassi-River example, but hornblende is more 

 abundant, making up about 70 per cent, of the rock. The specific 

 gravity is 3*10. This rock closely resembles the hornblende-gneiss 

 found by Mr. R. L. Reid in contact with the Monapo-River 

 crystalline limestone (p. 46). 



(4) Garnetiferous Gneisses and Eclogite. 



The garnetiferous hornblende-gneiss of the Ampwihi district 

 has already been described (p. 08), and two scapolite-bearing 

 garnet-rocks occurring in the Ampwihi and Memba districts have 

 been dealt with as products of contact between limestone and 

 gneiss (p. 49). A third scapolite-bearing rock from the district 

 north of the Xorray Hills is described below : for, as crystalline 

 limestone has not vet been found in that neighbourhood, its origin 

 cannot demonstrably be referred to contact processes. 



1 Am. Journ. Sci. ser. 4, vol. xl (1915) p. 427. 



