×

You are using an outdated browser that does not fully support the intranda viewer.
As a result, some pages may not be displayed correctly.

We recommend you use one of the following browsers:

Full text

Title
Transactions of the Symposium on Photo Interpretation

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)