﻿Vol. 66.~] OX THE GEOLOGY OP NYASALAND. 209 



mudstones, carbonaceous shales, and coals, presenting a total 

 thickness near the Mwapo Gorge of about 150 feet. These in turn 

 are overlain by a thick series of felspathic grits and sandstones, 

 containing pebbly seams near the top and one band of limestone. 

 The sandstones are followed by limestones and mudstones, which 

 abut directly against the Rukuru Ridge. 



While the Upper Grits and Sandstones are well represented, the 

 Lower Sandstone division appears to have thinned out very con- 

 siderably. Thus in the Mwapo stream, just below the gorge, only 

 some 15 feet of pale cream-coloured sandstones separate the Middle 

 Shale Group from the basement gneiss ; while farther north, where 

 conglomerates are developed, no hard-and-fast line can be drawn 

 between the Shale Group and the underlying beds. The only fossils 

 so far discovered were found in soft yellowish shales, associated 

 with coarse bluish grits belonging to the Upper Division : these 

 consist of Glosso2)teris[T]. 



Little is known of the Upper Mwapo basin. The Karroo here 

 appears to dip on the average in a north-easterly direction at fairly 

 low angles, except just along the northern ridge of gneiss, where 

 westerly dips up to 40° were noted. Basal conglomerates, including 

 two thin coal-seams, are exposed for a short distance in the Mwapo 

 stream, perhaps a mile above the gorge. The greater part of the 

 basin is, however, occupied by sandstones, presumably belonging to 

 the Upper Division. The character of the junctions with the gneiss 

 has not been clearly determined, but the evidence points to the 

 •existence of a double fault-line on the north, and perhaps also a 

 single fault along the southern boundary (see section 1, fig. 9, p. 218). 



The Sere basin is similarly bounded by a fault or faults on its 

 northern side. On the west and south-west, however, the junction 

 with the gneiss is a normal one. The basal Karroo is well exposed 

 in the Msampo stream, a tributary of the Sere, just below the lofty 

 Kayuni range. It is represented by lenticular boulder-beds, which 

 consist of subangular to rounded boulders measuring up to 2 feet 

 in length. Interbedded with these are fine red sandstones, overlain 

 by perhaps 200 to 300 feet of thinly-bedded greenish mudstones 

 with violet shales of smooth texture and well laminated. This 

 middle group of mudstones and shales contains no coal-seams or even 

 carbonaceous shale. It is followed by a great thickness of felspathic 

 sandstones and grits, which at one point include two thin seams of 

 earthy coal. The harder bands of this Upper Sandstone series 

 form low ridges running one behind the other, and rising towards 

 Kayuni Mountain. The usual dip is from east-north-east to north- 

 east at fairly low angles, which increase to 30° below Kayuni. 

 Westerly dips are sometimes noted near the northern fault-line. 



The Sere succession can be divided into the usual three 

 divisions. The Middle Shale Group, however, shows considerable 

 divergence from the usual type, and can only be described as 

 corresponding in position with that of the Lower Mwapo area. 

 The Upper Sandstones and Grits, on the other hand, agree closely 

 in character with those of the Mwapo-Ttukuru basin. 



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