WORKING GROUP 2 
STEPHENS 
103 
Lilongwe-Salima Area, Nyasaland 
In the Lilongwe-Salima area, Nyasaland, the regional strike of the meta- 
morphic rocks is north-north-east and there is an increase in metamorphic 
grade from north to south. The dominant rock types in the northern half of 
the area are micaceous schists and gneisses while granulitic rocks predominate 
in the south. The rocks have locally suffered alkaline metasomatism which has 
produced perthite enrichment. 
The paragneisses could be separated photogeologically into three main 
lithological groups based on topographic expression and photographic tone. 
The groups are well-defined in the north, but the lithological differences are 
less certain in the south, probably because of the overall increase in meta 
morphic grade. 
The first group, with chlorite-sericite gneiss as the typical rock type, forms 
fairly rounded hills with abundant grass, giving a light photographic tone. The 
dominant rock type is a pale micaceous gneiss containing muscovite, sericite, 
or chlorite. The rock is locally ferruginous when it forms steeper and higher 
hills capped by very short grass giving an identifiable off-white tone. 
The second group, with biotite gneiss as the dominant rock type, forms low 
undulating country. The photographic tone is darker than that of the previous 
group, because of an increase in the proportion of trees to grass. The biotite 
gneiss is generally leucocratic, with fine layers of quartz and feldspar giving a 
strong foliation to the rock. In the northern half of the area it was possible to 
delineate precisely the more leucocratic gneiss from the more melanocratic by 
Fig. 2. 
Stereopair: Quartzo-feldspathic ridge, Lilongwe-Salima Area, Nyasaland 
A ridge of folded quartzo-feldspathic gneiss in an area of leucocratic biotite gneiss. (Repro- 
ced by permission of the British Air Ministry, British Crown Copyright reserved)