﻿224 MESSES. A. It. ANDREW AND T. E. Q. BAILEY [May I9IO, 



Siliceous limestones with purple sandstones were observed near 

 Deep Bay, 320 feet above the lake ; while calcareous sands occur 

 400 feet above the lake, close to Mount Waller, on the new 

 Mission road to Port Stewart. 



From Mount Waller southwards comparatively little is known 

 of the actual border of the lake, our observations being mainly 

 restricted to hasty traverses. High-level gravel-deposits were, how- 

 ever, observed a few miles south of Chintetchi (fig. 1, p. 191), as 

 also at the entrance to the Dwangwa gorge and on the slopes of 

 gneiss behind the coastal plain of Kota Kota. Of these the 

 Dwangwa gravels lie some 400 feet above the lake, and were 

 obviously deposited by the Dwangwa Kiver on a gently inclined 

 rock-slope before its present gorge was cut. Some of the other 

 gravels occurring south of Mount Waller bear a similar relation to 

 the neighbouring rivers. It is, however, significant that well- 

 rounded gravel-deposits are almost, without exception, restricted to 

 the edge of the lake-basin. In the north, between Mpata and Mount 

 Waller, we have also seen that large patches of obviously lacustrine 

 gravels lie at an average height of 400 feet above the lake. Very 

 probably, therefore, the Dwangwa and other southern gravels were 

 formed at the mouths of rivers at a time when Lake Nyasa stood 

 some 400 feet higher than at present. 



The causes leading to the subsequent shrinkage in the lake have 

 not been sufficiently investigated. It is possible that a barrier, 

 some 400 feet high, once existed to the south of Liwondc in the 

 Shire Valley, and that this held back the waters of the lake until 

 it was cut through by the waters of the Shire. This, however, 

 fails to account for the 700-foot gravels, and it seems possible that 

 the whole effect may be due to earth-movement. 



2. Deposits occurring outside of the Lake-basin. — 

 These require but passing mention. Wide stretches of alluvium 

 have been formed by the Lower Shire and its tributaries in the 

 south of the Protectorate. Marls are met with occasionally in the 

 Upper Shire valley. Sandy loams are found to cover a great part 

 of Central Angonaland. 



The rarity of alluvial terraces and the paucity of gravels through- 

 out the country are worthy of note. 



Soils and Surface-Accumulations. 



The greater part of Nyasaland consists of plateau, covered with 

 surface-soil derived directly by weathering in situ. The character 

 of these accumulations naturally depends upon the underlying rock. 

 Where this consists of gneiss, the overlying soil is represented by 

 red, usually rather sandy, clays containing angular fragments of 

 quartz derived from the disintegration of the numerous quartz-veins 

 traversing the gneiss. These veins can be seen running up from 

 the underlying rock into the weathered clays above. While the bulk 



