﻿Vol. 66.] ON THE GEOLOGY OF NYAS ALAND. 199 



sandwiched in between high plateau-regions or steep ranges of 

 gneiss. It is obvious here that the Karroo owes its preservation to 

 faulting. In the south of the Protectorate rocks of Karroo age are 

 exposed along the eastern edge of a low broken plain which drops 

 gradually towards the Zambezi River. 



In the northern area the Karroo may be traced in isolated patches 

 from the Anglo-German border as far south as the southern 

 extremity of the Nyika Plateau. The prevalent dip of the series is 

 in an easterly direction, but occasionally the beds are thrown into 

 gentle anticlinal and synclinal folds. 



Trough-faulting is of common occurrence, and has the effect of 

 letting down long narrow strips of Karroo into the gneiss and schists 

 below. The dominant trend of these trough-faults is from north to 

 south. Not infrequently, the fault running along the western side 

 of these troughs dies out. In this case the prevalent easterly dip 

 of the Karroo in the faulted troughs or basins brings to light the 

 basal beds, which are invariably found resting unconformably upon 

 the older crystalline rocks. Owing to the patchy distribution of the 

 Karroo and the paucity of fossils, a close correlation of the beds 

 in the various localities cannot as yet be attempted. The Karroo 

 of Northern Nyasaland is, however, divisible into certain broad 

 divisions, which are recognizable with comparative ease : these are 

 as follows : — 



3. Upper Grit and Limestone Division. 

 2. Shale, Coal, and Mudstone Division. 

 1. Lower Sandstone and Basal Conglomerate Division. 



No fossils are known in Division 1. Division 2 has yielded fronds 

 of Glossojrteris; but, as a rule, the shales and mudstones of the coal- 

 group prove unprolific. In Division 3 fossils are more plentiful. 

 The massive grits themselves have only yielded one silicified tree- 

 trunk. Certain thin shale-bands in these grits, however, contain 

 leaves of Glossopteris, usually in a bad state of preservation. The 

 overlying limestones, where these are developed, are also associated 

 with fossiliferous shales from which fish-scales and lamellibranchs 

 have been obtained, first of all by Drummond near Mpata (B, fig. 2, 

 p. 193), and later by us in the Nkana (A, fig. 2) district some 20 

 or 30 miles north of Mpata. The limestones and mudstones which 

 Mr. Moore has called by the name of ' Drummond Beds ' are not, as 

 has been stated, unconformable to the lower grits of Division 3, but 

 rest upon the same with perfect conformity, and are probably of 

 Middle Karroo age. The apparent discordance which is to be 

 observed near Mpata is due to faulting. The Drummond Beds, 

 although of considerable thickness and importance, have not been 

 placed in a separate division. This is due to the fact that the lime- 

 stone group is missing in the faulted troughs on the west, and is 

 probably represented by grits, as the upper grits appear to thicken 

 considerably when traced westwards. 



Perhaps an ancient shore-line existed on the west : for, concurrently 

 with an increase in thickness of the upper grits, there is a decrease 



