﻿Vol. 66.] GEOLOGICAL STRUCTURE OF SOUTHERN RHODESIA. 367 



district, dark sandstones or quartzites were encountered, lying 

 unconformably beneath the coal-beds. These have only a small 

 outcrop, appearing as a ridge in the middle of the Coal Series. There 

 are also beds in the southern parts of the Wankie district that 

 appeared to me to be older than the Coal Series, although I was 

 unable to obtain definite evidence of their relation to the latter. 

 In the south-east of Mashonaland, however, the important cupri- 

 ferous deposits of the Sabi Valley are largely impregnations in a 

 series of sandstones and shales, 1 which are evidently older than the 

 coal-beds developed not far away to the south. These include 

 crumbly, white-weathering sandstones, which have below ground a 

 dark quartzitic appearance, very like the beds mentioned as occurring 

 at Mafungabusi. The associated shales are brown, grey, or purple, 

 and the whole character of the beds is almost identical with that of 

 the Waterberg Series (unfossiliferous) which underlies unconform- 

 ably the coal-beds of the Transvaal. There need be little hesitation 

 in correlating these shales and sandstones as of Waterberg age, for 

 the latter are known to cross the Limpopo from the Northern 

 Transvaal to the south-west of the area in question. 



Turning to newer rocks, the unconsolidated sands and gravels of 

 the Somabula Forest may be mentioned. These were first noticed 

 by myself in 1904, 2 and afterwards more fully described in 1906. 3 

 They are obviously later than the Forest Sandstones, the inferences 

 drawn from their lithological characters being fully confirmed by 

 the presence of abundant agate fragments derived from the basalts 

 of the Forest Sandstone Series. Pieces of the fibrous zeolite (either 

 scolecite or mesolite), which is so characteristic of the Victoria 

 Falls basalts, have also been noted. The sands of the Zambezi 

 Valley, apparently wind-blown, may be the equivalents of the 

 Somabula gravels, or of some part of the Forest Sandstone Series, 

 which also contains much wind-blown material. 



(a) The Older (? Waterberg) Sandstones. 



It is scarcely possible to add much to the scanty information 

 regarding these rocks already given in discussing the general 

 question of classification. They probably cover a considerable 

 extent of country in the Sabi basin and also farther west, but it is 

 not possible to make any definite assertion on the point. North of 

 the high plateau they are not well developed. The northern portion 

 of Mashonaland is apparently devoid of sedimentary beds altogether, 

 except possibly along the banks of the Zambezi, as I have been fairly 

 close to its northern border in the Lomagundi and Mount Darwin 

 districts without encountering any. Westward, however, the north 

 of Matabeleland provides the most extensive sedimentary area of 

 Rhodesia, and we find these beds exposed as already noted, pro- 

 truding through the coal-beds between the Dimdimutwe and Gungwe 



1 ' Science in South Africa ' 1905, p. 302. 



2 ' Geology of Southern Rhodesia' 1904 (Spec. Rep. No. 2,Rhod. Mus.) p. 17. 

 ' A Geol. Mag. dee. v, vol. in HOOW pp. 459-«2. 



