Vol. 65.] KARROO SYSTEM IN NORTHERN RHODESIA. 427 



accounted for by the grinding together, even in the absence of 

 ice. jNo other features that might be put down to glaciation were 

 observed. 



Strain-fractures and joints shape out the mass into blocks, and 

 fissures pass through pebbles and matrix alike, resulting in clean- 

 cut faces, over which quartz-crystals have grown. Parallel crush- 

 cracks are induced for a few inches on each side, and cause the 

 rock to yield an angular debris when it breaks up. 



At Chigona the vertical joints run E. 10° S., the tabular joints 

 dipping 10° east-south-eastwards. The dip is generally tangential 

 to, and away from the domes of Archaean rocks upon which the 

 conglomerates abut. 



Among the basal beds of the system — those lying between the 

 base of the Lower Matobola Beds and the floor — must be mentioned 

 the unstratified red sandy clays at Chisalisali (PI. XXI). They have 

 many crush-cracks and small slickensides in all directions, the chief 

 being to the west. They have an ascertained thickness of 100 feet, 

 and are overlain by nodular concretions of haematite in definite 

 bedding-planes, in an otherwise unstratified mass of red clays. These 

 weather out in the bed of the Molongushi Elver in rounded masses, 

 and the first river-floods of the summer are coloured pale blood- 

 red by their decay. Similar strata occur under the coal-measures 

 west of Kalilingoma, at Impala Kidge, and Muchinda Valley, 

 containing pipe-clays, fibrous gypsum, and pisolitic ironstone. 



The Lower Matobola Beds or the Coal Series. 



These follow conformably upon the previous series. The whole 

 succession of the coals and clays can be splendidly seen in the bed 

 of the Molongushi at Chisalisali, where the river cuts across the 

 strike for over 2 miles : the abrupt manner in which the coal-beds 

 commence over the basal nodular clays is seen in PI. XXI. The 

 thickness is here 400 feet, and the seams of coal number upwards 

 of 100 — the widest being over 6 and 8 feet— and range downwards 

 to a few inches only. 



The coal is made up of laminae of dull black shaly matter with 

 bright shining coal — so numerous as to be almost microscopic. The 

 latter frequently increase to as much as 3 inches in thickness, and as 

 these parts contain only 3 or 4 per cent, of ash, their predominance 

 greatly improves the economic value of the fuel. The dull layers 

 seem, at first view, to be only shale, but their faces are covered 

 with the powder known as ' mother of coal.' The bright matter 

 splinters easily, and decrepitates on drying, fracturing in concentric 

 rings or conehoidally. It has been known to yield balls measuring 

 half an inch in diameter that weathered in concentric foliae ; while 

 another specimen shows a number of discs, like the fractured ends 

 of a bundle of thin pencils. 1 



1 This structure resembles that of the Scottish 'eenie' coal, described by 

 Messrs. O. T. Olough & J. Kirkpatrick in Trans. Inst. Min. Eng. vol. xxxvii 

 (1909) pp. 2-11. 



