﻿Yol. 66.] GEOLOGICAL STRUCTURE OF SOUTHERN RHODESIA. 365 



IV. The Unaltered Sedimentary Rocks. 



The group of sediments that have now to be considered is a some- 

 what troublesome one to deal with. They do not occur (apart from 

 certain outliers of the uppermost strata) anywhere in the more 

 settled and accessible parts of the country, and, moreover, they 

 afford few sections from which the relationships of the different 

 divisions can be recognized. Most of the country is covered to a 

 depth of many feet by loose sand resulting from the disintegration 

 of the underlying rocks, so much so that one can travel for miles 

 without seeing a stone. Moreover, owing to the absorbent nature 

 of this sandy covering, there are practically no permanent water- 

 courses over large areas, and this not only implies few exposures, 

 but renders travel itself a matter of the utmost difficulty. 



The first rough classification of these rocks was suggested by 

 myself in the First Annual Report of the Rhodesia Museum (1902- 

 03, p. 9). In this I proposed to recognize two main divisions : the 

 Coal Series, and the beds above the Coal, or the Zambezi Series. 

 Almost immediately afterwards, Mr. A. J, C. Molyneux, in a paper 

 read before this Society, made a much more elaborate classification, 1 

 which may be summarized as follows : — 



Zambezi Basin : — 



Thickness in feet. 



Thaba-s'Induna Series 2(W 



Forest Sandstones, with basalts 1000 



Escarpment Grits 400 



Upper Matobola Beds (with coal-bearing beds) 300 



Busse Series (local only ?) 300 



Lower Matobola Beds (with coal-bearing beds) 200 



Sijarira Series 2000 



Limpopo Basin : — 



Tuli Lavas. 

 Coal-bearing Beds. 

 (Unconformity.) 

 Samkoto Sandstones. 



Before dealing with the characters and distribution of the rocks, 

 it is necessary to discuss their classification. It may, first of all, 

 be noted that no fossils except silicified wood are found in any of 

 the beds, except in those associated with the coal. In the Upper 

 Matobola Beds occurs Palceomutela keyserlingi, also found in the 

 Permian of Russia and in the Middle Beaufort {Dicynodon Beds) of 

 the Cape. In the Busse Beds are found Acrolepis molyneuxi (a 

 fish) and impressions of Sigillaria and Calamites. If, therefore, 

 we accept the succession tabulated by Mr. Molyneux, the productive 

 coal-measures at Sengwe are apparently on a considerably lower 

 horizon than the Ecca Beds of the Cape, which are characterized by 

 Glossopteris. The Coal Series at Wankies has yielded impressions 

 of Vertebraria* but this is from a higher horizon than the coal. 



1 Quart. Journ. Geol. Soc. vol. Hx (1903) pp. 275 & 278. 



2 Gr. W. Lamplugh, ibid. vol. lxiii (1907) p. 176. 



