﻿Vol. 66.~] GEOLOGICAL STEtTCTTTEE OF SOTJTHEEN EHODESIA. 353 



14. The Geological Stetjctuee of Sotttheen Rhodesia. 

 By Eeedeeic Philip Mennell, F.G.S. (Read December 1 5th, 1909.) 



[Plate XXVIII— Geological Map.] 



Contents. 



Page 



I. Introductory 353 



II. The Metamorphic Rocks 354 



III. The Granite Masses, and their Relations with the 



Metamorphic Rocks 362 



IV. The Unaltered Sedimentary Rocks 365 



V. Various Igneous Rocks 371 



I. Inteodttctoey. 



The region popularly denominated ' South Africa ' is usually con- 

 sidered as extending from the Cape to the Zambezi River, and the 

 latter is also the dividing-line between Northern and Southern 

 Rhodesia. The South African area is made up principally of sedi- 

 mentary rocks, which include an unbroken stratigraphical sequence 

 from the base of the Devonian up to the Jurassic System. Even at 

 the Cape, however, inliers of older rocks are exposed, which cannot, 

 as palgeontological evidence is lacking, be ascribed with certainty 

 to any particular period. These ' Pre-Cape ' rocks become increas- 

 ingly important as the Transvaal border is approached ; and in the 

 southern part of that province we find, developed along the denuded 

 axis of a great anticline, those ancient strata of the ' Transvaal 

 System ' which include the gold-bearing ' banket.' 



These old rocks have been subdivided into a number of separate 

 groups, each of great thickness and all probably of Archaean age. 

 They still present a comparatively normal sedimentary facies 

 however, and it is only in places, towards the north, that we find 

 areas of crystalline schists, associated, as usual, with huge granite 

 masses. In fact, it is only near the Rhodesian border that we enter 

 upon that great region of metamorphic schists which appears to 

 occupy most of the central portion of the African continent. So 

 limited is the distribution of unaltered stratified rocks over the 

 greater part of this area that Mr. J". A. Chalmers & Dr. F. H. Hatch, 

 in publishing the first brief references to the geology of Rhodesia, 1 

 could only record, after a by no means insignificant amount of 

 travel, that sediments are ' said to occur.' The present writer, with 

 more extended opportunities of investigation, has been led to 

 compare the sediments with the drift-deposits of England, 2 and the 



1 Geol. Mag. dec. iv, vol. ii (1895) p. 195. 



3 ' Geology of Southern Rhodesia ' 1904 (Spec. Rep. No. 2, Rhod. Mus.) p. 25. 



