﻿Vol. 66.~\ THE GEOLOGY OF NTASALAND. 219 



(A) Sumbu Section, from the Mwanza River in the east 

 to the ^Tkombedzi wa Chuma, along the African 

 Transcontinental Telegraph line (or across A'A of the 

 map, fig. 8, p. 216). 



The junction of the Karroo with the gneiss is obscured by the 

 alluvium of the Mwanza River, but is evidently a faulted one. 

 The lowest beds exposed, although they belong to the Lower Sand- 

 stone Group, dip eastward towards the gneiss. The exposures are 

 poor at first ; but, on travelling westwards, the sandstones are clearly 

 seen to be thrown into a series of gentle anticlinal and synclinal 

 folds with occasional dips of #0° to 40°. Some 4 miles from Sumbu 

 the beds begin to dip steadily westwards at an average angle of 

 about 15°. The bulk of the Lower Sandstones are massive and 

 usually current-bedded. Pebble-beds are of common occurrence,, 

 though sometimes only one pebble thick. Curious large cavities 

 resembling pot-holes occur in places : these sometimes contain 

 water, and were probably formed by a partial rotting away of the 

 sandstone, consequent upon water collecting in original slight 

 depressions on the surface. The sandstones are often felspathic 

 or slightly calcareous, and are thus somewhat readily attacked and 

 disintegrated. The whole group is from 6000 to 7000 feet thick. 

 The shales of Group 3 come on to the west near Sumbu, and form, 

 a low tract of ground below the undulating sandstone country. 

 The shale group consists of the usual fine-grained sandstones and 

 black and grey mudstones, with thin seams of coal and ironstone.. 

 The average dip is about 8° westwards. Fossil leaves of Glosso- 

 pterls are comparatively common, and numerous specimens may be 

 obtained near the telegraph- track at Sumbu. Only a small part of 

 the Upper Sandstone Group is exposed along the line of traverse. 

 The Upper Sandstones follow conformably on the shales, without 

 any change in contour of the ground. A number of pebbles 

 of compact earthy limestone of recent origin are scattered in 

 places over their weathered surface, and similar material is found 

 filling cracks in the more calcareous bands. The sandstones dip. 

 westwards, but become almost horizontal on the north. 



(B) Murukunyama Section, from near Panyanole's Til- 

 lage on the Tangasi, through Panga village to near 

 Kasembe Hill on the west (or roughly along the line 

 B'B of the map, fig. 8, p. 216, and section 3, fig. 9, p. 218). 



Proceeding westwards, the following groups are seen to be 

 exposed : — 



(3) Shale Group. — The members of this group are faulted 

 against the gneiss on the east and only some 500 feet are seen.. 

 The actual fault-line is occupied by a drusy quartz-band, which 

 sometimes passes into a siliceous breccia containing fragments of 

 silicified sandstone. This fault-vein is of great width, and forms 

 a line of hills separating the gneiss from the Karroo. Somewhat 



