﻿236 MESSES. A. R. ANDREW AND T. E. G. BAILEY [May I9IO, 



large deltas projecting for considerable distances into the lake also 

 points to the relatively recent origin of the lake-depression. On 

 the other hand, the gorges of the Southern Rukuru, the Bua, and 

 several other rivers are of considerable depth and many miles in 

 length. These have been cnt as a consequence of the formation of 

 the Rift Valley, and are clearly not the work of a day. 



Y. Conclusions. 



1. The greater part of Nyasaland consists of crystalline rocks 

 which comprise : — 



(A) Highly metamorphosed sedimentary beds, including graphitic gneisses 



with limestones, and quartz- and muscovite-schists. 



(B) Foliated igneous rocks, especially augen -gneiss derived from granite 



or syenite. 



(C) Plutonic intrusions, usually granite or syenite, more rarely norite or 



gabbro. 

 Nepheline- and sodalite-syenites are found in two localities, and are 

 possibly identical in age with the similar post-Waterberg and 

 pre-Karroo syenites of the Transvaal. 



2. In the north-western corner of Nyasaland a somewhat altered 

 sedimentary series forms the Mafingi Hills. This series consists 

 of a great thickness of quartzites, grits, and sandstones, and is of 

 pre-Karroo age. 



3. Rocks belonging to the Karroo System are found both in 

 Northern and in Southern Nyasaland. In the north the Karroo is 

 of patchy distribution, and owes its preservation to faulting. It 

 is evident that the Karroo had formerly a much wider distribution 

 in this area than at the present time. 



Freshwater lamellibranchs belonging to the genus Palwomutela 

 and also fish-scales of Colobodus occur in the calcareous group of the 

 north, while species of Olossopteris were discovered in the Karroo of 

 "both areas. 



The Karroo of Nyasaland is comparable with that of Rhodesia 

 and German East Africa. 



4. Recent lacustrine marls and sands are found at distances of 

 15 miles and under from the north-western margin of Lake Nyasa, 

 and occur to great heights above its present level. 



5. Pumiceous tuffs associated with recent gravels containing 

 pebbles of Tertiary lava are found in the extreme north of the 

 country. Across the border, in German East Africa, Tertiary and 

 recent lavas and tuffs have a wide distribution. 



6. Nyasaland consists of high plateau-regions rising irregularly 

 one above the other. The Nyika and Vipya plateaux were, doubt- 

 less, at one time continuous, and formed a platform of erosion 

 produced at a time subsequent to the main faulting of the Karroo 

 in Northern Nyasaland and previous to the formation of the great 

 Nyasa depression, which is regarded as a true ' rift valley '. 



