548 C. B. Horicood ^ A. Wade — The Old Granites of Africa. 



that any extensive area of moderate slope is covered with, granitic 

 soil, its quality is beyond dispute. He points out that the hij^h 

 angles of the slopes in a rugged granitic country accelerates the 

 drainage from the soils, where they are present, of all the alkalies 

 in solution, as well as the other soluble chemical ingredients, which 

 are necessary to the formation of a productive soil ; also that in 

 some parts of the world granitic soils are of extreme richness from 

 the presence in the granite of apatite, a mineral which is a natural 

 phosphate. 



These granitic areas are generally Avell watered, as, for example, 

 in Natal and Zululand, the Johannesburg-Pretoria boss, the Limpopo 

 region, and the Uelle and Lado Enclave provinces of the Congo 

 Pree State. Grold occurs in quartz -veins in the Old Granite in the 

 Zoutpansberg disbict. At the Ayrshire mine ^ in Ehodesia gold 

 occurs in an augite-diorite dyke traversing the granite. Tin occurs 

 in pegmatite dykes in the Old Granite in Swaziland, at Embabaan ; 

 also in veins in the granite at Kuils Eiver, near Cape Town. 

 Probably payable deposits of kaolin, derived from the decomposition 

 of the Old Granite, will in time be discovered. 



CoNCLTJsioisrs. 



Prom the foregoing the following conclusions are derived : — 



(1) In South and Central Africa there exists a Pundamental Granite- 

 Gneiss Pormation, which formed the nucleus or core of the continent, 

 the base of the geological column on and around which the younger 

 formations have been built up, and although later portions are 

 intrusive in the Swaziland Series, nevertheless it underlies and 

 supports it in much the same way that the Pundamental or Laurentian 

 Gneiss of Canada is intrusive in and yet underlies and supports the 

 Grenville Series.- In Eastern Canada, however, the original basement 

 upon which the first sediments were laid down has nowhere been 

 discovered, having been everj^where torn to pieces by the Laurentian 

 Granite intrusions ; ^ whereas in South Africa later portions of the 

 Old Granite are intrusive in both the Pundamental Gneiss and alsa 

 in the oldest existing sediments, and there is no reason to assume 

 the pre-existence of still older sediments ; but, as we have seen, there 

 is good reason to regard the Old Gneiss as the original basement on 

 which the oldest existing sediments were built up. This Pundamental 

 Granite- Gneiss Formation is especially well developed in the region 

 of the Limpopo, in German South-West Africa, in German East 

 Africa, in parts of the Congo Pree State and of the Nile Basin, in 

 Mashonaland and Matabeleland, and also in Natal and Zululand. 



(2) It follows from (1) that the Old Granites of South Africa, 

 although all derived from similar, probably the same, magma, are not 

 all of exactly the same age. Thus it would seem that the Old Granite 



1 The Geology of South Africa, by Hatch & Corstorphine, 1905 (Macmillan & Co.) , 

 p. 105. 



- " On the Structui'e and Relations of the Laurentian System in Eastern Canada," 

 by Professor F. D. Adams, D.Sc, F.R.S. : Quart. Joiirn. Geol. Soc, vol. kiv. 

 No. ccliv, p. 146. 



3 Loc. cit., p. 147. 



