546 C. B. Eonvood 8f A. Wade— The Old Granites of Africa. 



quartzites, jasperoid rocks, and conglomerates which are present in 

 the west of Zululand in the Nkandhla and Tugela Valley districts. 

 The petrological character and mineralogical composition of the granites 

 forming these erratically disposed areas usually varj^ much, and there 

 seems little doubt that the gneissic and schistose series of rocks is of 

 a much greater age than the metamorphic rocks, quartzites, jasperoid 

 rocks, etc., above mentioned, and probably represents the oldest rocks 

 of the Continent, the original basal series of this part of the world, 

 which formed the backbone of Africa upon and around which all the 

 younger sedimentary formations have been deposited." 



He then says: "Whether this most ancient series of granites, 

 gneisses, and schists are the same as the Namaqualand gneisses and 

 schists I cannot yet say, but my friend Dr. Corstorphine informs me 

 that lately he has identified a similar series of granitic gneisses and 

 schists on the Limpopo River, to the north of Pietersburg. His 

 description of the occurrence and character of these rocks on the 

 Limpopo tallies exactly with this series on the East Coast which 

 I have just mentioned." 



Having now passed in review the most important work done on the 

 Old Granites of South Africa during the last ten or eleven years, 

 before summarizing the chief deductions which may be drawn from it, 

 I will, very briefly, say a few words on the scenic and economic 

 aspects of the gneiss and granite areas. 



Scenic and Economic Aspects. 



In describing the pre-Cape rocks of the south and west of Cape 

 Colony, Mr. Rogers ^ states that the masses of granite and gneiss form 

 the highest ground, with the exception of outliers of Table Mountain 

 sandstone. In Griqualand West and Prieska they form most of the 

 lower-lying country, seldom rising far above the generally sandy ground 

 in hills or ' tors ' as the granitic rocks do in Bushmanland and in the 

 south-west districts of the Colony.^ I have also noticed this feature 

 of the granite country in the Prieska district, and have observed that 

 as one travels further east the granites of Upington and of Southern 

 Gordonia, generally near the borders of German South- West Africa, 

 frequently rise into ' tors ' or bare rugged hills, especially the more 

 massive varieties. 



In the Congo territory described by Preumont and Howe ^ the 

 country is, of course, mostly covered with equatorial forest and the 

 ground with a heavy layer of surface soil, so that outcrops are few 

 and far between. The greatest elevations (3300 to 4000 feet) are 

 attained in the Mle-Congo watershed. In the south-east and north- 

 east the country is hilly or even mountainous ; westwards it gradually 

 becomes lower and monotonous, with broad undulations, out of which 

 rise in places groups of isolated hills. A large extent of the Uelle 

 district is very densely wooded ; to the north of this forest area it 

 consists of vast plains covered with grass and scrub, pierced by broad 

 valleys covered with forest growth following the watercourses. 



' The Geology of Cape Colony, bv A. W. Eogers, 1905 (Longmans, Greeu, & Co.), 

 p. 38. 



^ Loc. cit., p. 64. ^ Loc. cit., p. 643. 



