C. B. Horivood 4' A. Wade— The Old Granites of Africa. 501 



"With reference to these lines of crush he says: "they consist 

 mainly of reefs of massive vein-quartz, which forms their central 

 portion, and this is usually flanked on either side by a narrow zone of 

 crushed and highly-sheared vein-quartz and granite, both kinds of 

 rock being often brecciated and crushed together. The central 

 portions have also frequently been fractured and brecciated, the 

 fragments having been recemented by a secondary deposition of 

 siliceous material." He instances one which extends for a distance 

 of 12 miles and occurs about half-way between the eastern and 

 western boundaries of the granite mass. This sheared and crushed 

 nature of the granite along its marginal portions and along the edges 

 of the quartz reefs he attributes to earth-movements subsequent to the 

 consolidation of the granite. 



In September, 1905, Dr. F. AV. Yoit ' briefly described the 

 occurrence of various gneisses, such as mica, hornblende, protogine, 

 augen, flaser, epidote, and garnet gneisses, granulites, eclogites, and 

 similar rocks, which occupy vast areas in the Northern Transvaal, 

 including the Limpopo Flats. He suggested that all the phenomena, 

 including petrographical character of the rocks, their monotony, and 

 enormous extension probably indicated that they represented a Funda- 

 mental Formation ; perhaps a vast area of original granite which had 

 been converted into gneiss as a result of enormous pressure. The 

 following month, in a paper entitled "Gneiss Formation on the 

 Limpopo",- he points out that in such an old and large continent 

 we have reason to expect that there should exist a Fundamental 

 Gneiss Formation, and that the petrographical character of the rocks 

 of the Swaziland Series, in which the Old or Basement Granite is 

 intrusive, is such that we cannot class them among those rocks 

 which elsewhere are considered as constituting the basement or 

 fundamental rocks on which the othei's have been laid down. That, 

 in fact, this Swaziland formation very largely consists of arenaceous 

 and argillaceous rocks, which must have been derived from a still 

 older formation. 



He then shows that such a formation, consisting of granite and 

 gneiss, actually occurs and covers an area of at least 800 square 

 miles in the Limpopo Basin. He tells us that the formation for the 

 greater part consists of ditferent varieties of gneisses and schists, 

 among which also occur hornblende and pyroxene rocks, crystalline 

 limestones, quartzites, haematites, and magnetites. The gneiss, he 

 says, shades off into a non-foliated rock, which occurs in alternating 

 bands, but is structurally a granite, and is only sparsely developed 

 in comparison with the foliated rocks, and evidently belongs to the 

 period and process of the granite formation, and cannot be looked 

 upon as a later intrusion. He describes the gneissoid rock as being 

 an aggregate of flesh-red oi'thoclase, quartz, and a greenish somewhat 

 decomposed hornblende, the minerals occurring in long, stretched, 

 alternating individuals, with a strictly banded arrangement, and 

 sometimes showing evidence of having undergone much pressure ; 



1 " Preliminary Notes on ' Fundamental Gneiss Formation ' in South Africa," by 

 Dr. Voit: Trans'. Geo!. Soc. S.A., 1905, vol. viii, pp. 106-7. 



2 Trans. Geol. Soc, 1905, vol. viii, pp. 141-6. 



