﻿Vol. 66.] ON THE GEOLOGY OF NYASALAND. 195 



The plutonic rocks, for convenience of description, may be 

 roughly divided into the following three classes : — 



Class (i). — Foliated intrusions which lie, with the exception of the Dzala- 

 nyama granite, to the north of latitude 14° S. 



Class (ii). — Unfoliated intrusions which are found, for the most part, south 

 of latitude 14°. 



Class (iii). — Certain coarse-grained intrusions of acid granite. 



The foliated plutonic intrusions grouped under Class (i), while 

 differing widely among themselves in age, show certain common 

 characteristics which allow of their separation into a distinct class. 



They consist, for the most part, of granite or syenite with well- 

 developed porphyritic crystals of felspar. The granites rarely 

 contain much quartz, and resemble the associated syenites in the 

 abundance of microcline, and the occurrence, at times, of perthitic 

 felspars. The great granite intrusion which forms the central 

 portions of the Nyika Plateau is of somewhat peculiar type, 

 consisting of large felspars of acid plagioclase, microcline, etc., 

 quartz, and a very little biotite. The felspars show a parallel 

 arrangement, but are otherwise unaltered. The quartz, however, 

 appears to have been crushed and converted into a granular 

 aggregate, the indivinual granules of which are just visible to the 

 naked eye. 



In the Fort Manning range of Central Angonaland a dark even- 

 grained granite occurs, in which the quartz is of a blue or smoky 

 colour. Pyroxene appears to be a fairly common constituent of 

 this rock. 



Class (ii). — Under this heading are included the huge boss-like 

 intrusions which compose the high plateaux of Zomba and Mlanje. 

 Though superficially isolated, there can be no doubt that the Zomba- 

 Mlanje masses, in common with the large intrusion to the east of 

 Lake Pamalombe, are genetically related. The Mlanje mass is 

 built up of hornblende-granite, which consists of microperthite and 

 other felspars, hornblende and a little quartz. The crystals of 

 hornblende may reach several inches in length in the coarser 

 varieties of the Mlanje granite. The Zomba mass consists of 

 granite and syenite of similar type. A marginal modification is 

 found about 7 miles from Liwonde, on the Liwonde-Zomba road. 

 This is a banded syenite, rich innepheline and occasionally sodalite. 

 Hornblende sometimes occurs in the form of very long lath-shaped 

 crystals, grouped together in veins crossing the syenite. The last 

 stages of intrusion are represented by numerous nepheline-bearing 

 dykes which traverse the syenite and the adjacent gneiss. A very 

 similar nepheline-sodalite syenite, of a beautifully blue colour, is 

 found far to the north in the Nyika Plateau : sodalite is here an 

 abundant constituent. 



Basic intrusions of plutonic rock are of rare occurrence. Certain 



