408 MR. A. J. C. MOLYNETIX ON THE [Aug. I 9°9> 



22. On the Karroo System in Northern Rhodesia, and its Rela- 

 tion to the General Geology. By Arthur John Charles 

 Molynetjx, F.G.S. (Read February 24th, 1909.) 



[Plates XVII-XXIIL] 



Contents. Page 



I. Introduction 408 



II. Physical Features 409 



III. The Karroo System 421 



IV. Structural Geology 430 



V. Physical History 434 



VI. Subaerial Decomposition in the Luano ... 436 

 VII. Conclusion 437 



I. Introduction. 



In 1903 (in vol. lix of this Journal) I described the occurrence 

 in Southern Rhodesia of deposits of Permo-Carboniferous age that 

 have since been correlated with the Karroo System of South Africa. 

 In the present communication will be traced their extension into 

 Northern Rhodesia. There they are found occupying the lowlands 

 of the Zambesi basin, and they also constitute the floors of the 

 trench-like valleys of the Lusenfwa River (or Luano plains), 

 of the Lukasashi River, and probably of the Luangwa. These 

 depressions form a more or less continuous succession of troughs 

 bisecting Rhodesia diagonally, along a distance of some 800 miles, 

 that is, from the Deka River to the head of the Luangwa. They 

 lie some 2000 feet below the surrounding country, which is of 

 plateau type and is made up of metamorphic and crystalline rocks 

 of the pre-Karroo complex. The change from upland to valley- 

 plains is generally abrupt, giving rise to steep escarpments that 

 appear as mountains when viewed from the lower position. 



Nowhere, so far, in the vicinity of these depressions have ' high- 

 level ' areas of Karroo rocks been met with on the plateau, and 

 one's first impression is that these basins are vestiges of an original 

 landscape, in which the sediments were deposited. But we have 

 been prepared by Mr. G. W. Lamplugh, in his description of the 

 Deka Fault, 1 for great displacements of Karroo strata and earth- 

 movements, and there is ample evidence to show that these valleys 

 and low-lying regions of sediments are largely due to important 

 folding which took place in post-Karroo times. 



Apart from its tectonic aspect, the question of original difference 

 affects the economics of the coal-distribution of Rhodesia. If these 



1 ' Geology of the Zambezi Basin around the Batoka Gorge (Ehodesia) ' 

 Quart. Journ. Geol. Soc. vol. lxiii (1907) p. 162. 



