﻿222 MESSES. A. E. ANDEEW AND X. E. O. BAILEY [May I9IO, 



of sandstones, is reminiscent of the Karroo sequence in the Mwapo 

 and Western JNyika areas. On the other hand, the Tuli and Batoka 

 lavas can only be compared with those found in the Lower Shire 

 district. The Karroo of Ehodesia, as regards its general characters, 

 seems, in consequence, to occupy an intermediate position between 

 the Northern and the Southern Karroo of Nyasaland. 



The Tuli and Batoka basalts which occur at the top of the 

 Ehodesian Karroo are now considered to be of Stormberg age, and 

 there can be little doubt that the similarly placed lavas of Southern 

 Nyasaland may also be roughly referred to this horizon. Up to the 

 present, lavas (belonging to the same regional outbreak of vulcanicity 

 in Stormberg times) are knoAvn in Cape Colony, the Transvaal, 

 Ehodesia, and Nyasaland : their northern limit has yet to be denned. 

 In the Karroo of Cape Colony a series of sandstones, shales, con- 

 glomerates, etc., amounting in all to about 1400 feet in thickness, 

 are found to underlie the Stormberg lavas. 



Traced northwards, the various groups included in this series 

 appear to thin out considerably, so that in Ehodesia the minimum 

 thickness of the whole Karroo System is put at about 4700 feet. It 

 is interesting, therefore, to find that the system swells out again in 

 Southern Nyasaland to a thickness even exceeding the 18,100 feet 

 given as a maximum figure for the Cape Colony Karroo. This 

 thickening of the Karroo appears, however, to be a comparatively 

 local phenomenon, restricted, so far as we know, to the Lower Shire 

 district and to the adjoining portions of Portuguese East Africa. 



(3) Eecent Deposits. 



These may be divided into (a) volcanic and (/3) sedimentary 

 deposits. 



(a) Volcanic deposits. — Tertiary and recent lavas occur 

 immediately north of the Songwe Eiver in German territory. 

 According to Dr. Bornhardt, these comprise basalts, andesites, and 

 trachytes. The lavas are overlain by tuffs, which mark the final 

 phases of volcanic activity in the district. 



Lavas of recent age are not known in Nyasaland, but a small 

 patch of pumiceous tuff is found banked up against the eastern wall 

 of the Nkana Valley in the extreme north of the country (fig. 3, 

 p. 202). This tuff is associated with gravels containing pebbles of 

 trachyte, phonolite, and other volcanic rocks. Blocks of tuff are 

 also found near Chungu, on the southern edge of the Songwe flats, 

 and about 9 miles east of Nkana. These blocks are probably 

 remnants of a sheet of tuff which has been removed by erosion. 



(/3) Sedimentary deposits. — These may be grouped under 

 two heads : — 



1. Deposits within the Lake-basin. 



2. Deposits occurring outside of the Lake-basin. 



