﻿194 MESSRS. A. E. ANDREW AND T. E. G. BAILEY [May I9IO, 



A very distinctive group of rocks forms the eastern portions of 

 Central Angonaland. This consists of graphitic gneisses interbanded 

 with fine-grained felspathic gneiss, thick beds of crystalline lime- 

 stone and kyanite-schists, the two last-named frequently containing 

 flakes of graphite. The graphitic gneiss consists of quartz and 

 felspar, with numerous flakes of graphite scattered throughout the 

 mass. Occasionally this graphite is concentrated into veins and 

 lenticles, and in such cases the gneiss is more or less kaolinized. 



The limestones are highly crystalline and generally impure.. 

 The crystalline impurities consist for the most part of diopside and 

 forsterite, the latter now largely converted into serpentine. Prom 

 the abundance of such impurities it is evident that the limestones 

 were originally dolomitic in character. Impure calcareous bands,, 

 rich in garnets and lime-silicates, are found in association with these- 

 limestones. 



The kyanite-bearing gneisses are generally coarse-grained, and 

 consist of quartz, felspar, white mica, and graphite. The kyanite 

 frequently forms crystals exceeding an inch in length, and is usually 

 dirty grey in colour, but sometimes blue. Stringers of limonite are 

 common in these gneisses. In certain localities, as, for instance, 

 near Chiwambas on the Lilongwe River, the graphitic gneiss contains 

 numerous sill-like masses of garnet'-amphibolite, a dark, well- 

 crystallized rock composed of hornblende and large red garnets. 



This series of graphitic gneisses and limestones can be traced 

 southwards for a considerable distance down the Shire Valley, and 

 is again met with in the Port Herald district. Graphitic gneisses 

 are also known in a detached outcrop to the north, near Usisya, on 

 the coast of Lake Nyasa. 



Among gneisses of more doubtful origin may be included well- 

 banded hornblende, biotite, quartz-felspar gneiss, felspathic gneisses, 

 in which ferromagnesian minerals are rare, and garnet-gneisses 

 and granulites. Gneisses and schists of obviously igneous origin 

 are well developed. In the Nyika and Vipya areas, bands of 

 talcose schist, sometimes of considerable thickness, probably repre- 

 sent basic intrusions. Chiramimbi Hill, near Fort Manning, is. 

 composed of serpentine converted in places into talcose schist. 



Fine-grained gneisses with platy structure may be traced in the 

 field through every gradation into augen-gneiss, which in turn is 

 found to pass into slightly foliated syenite or granite. Augen- 

 gneiss, obviously of granitic origin, is of common occurrence in 

 Northern Nyasaland, where it forms narrow sill-like lenticles in 

 the steeply dipping schists and gneisses, and also broad bands 

 several miles across. 



Plutonic intrusions. — It is impossible to draw any hard-and- 

 fast line between the augen-gneiss and the plutonic intrusions, for- 

 iri many places, as already stated, the one passes into the other. 



