544 C. B. Horuood Sf A. Wade — The Old Granites of Africa. 



schistose rocks were laid down on an old fundamental basement granite 

 before the earth-movements occurred which induced the gneissoid 

 structure of the granite ; and it is therefore to the same causes which 

 produce this gneissoid character that the schistose and foliated nature 

 of these rocks is due.^ Further, that the gneiss and schists have been 

 so fractured, crumpled, and tilted, that a pseudo-stratification or 

 interlamination of gneiss and schists has been produced. 



Mr. Holmes has shown that these earth-movements have certainly 

 extended up to later times than the Pretoria period. Thus, with 

 reference to the South-Western Transvaal, he writes ^ — 



"The most noticeable feature in the structure of this part of the 

 country is a folding of the formations, the axis of which has a general 

 north and south direction, due to pressure acting east and west. The 

 main axis passes near Schweizer-Reneke northwards to the Kunana 

 Reserve, along which line we find exposures of the primary granite. 

 This line also divides the two great synclines of Dolomite and Pretoria 

 Beds, one of which extends over the Kaap Plateau in Bechuanaland 

 and the other over the North-Western Transvaal in the Marico and 

 Rustenburg districts. 



" It is noticeable that this axis is coincident with the lamination of 

 the gneiss, and that the pressure was prolouged in the same direction 

 for a long period, acting most intensely on the oldest rocks ; thus, 

 whereas the quartzites immediately beneath the diabase at Schweizer- 

 Reneke show comparatively gentle folding, the shales of Abelskop are 

 crushed and folded to a great degree in the same direction." 



I find that Mr. A. W. Rogers,^ in describing the 'Keis Series * of 

 Cape Colony, has given expression to a similar opinion with reference 

 to the granite and gneiss and the quartzites and mica-schists which 

 compose the 'Keis Series. He says — 



" Along the greater part of their course the 'Keis Beds are flanked 

 on either side by granite or gneiss, and areas of these rocks also 

 occur in the heart of the series at Kaboom, Brakbosch Poort, and 

 probably other places. At Boschiesman's Berg and Van Wyk's Pan 

 tongue-shaped masses of gneiss project into the series from the great 

 granitic area. These tracts of igneous rock are elongated in the 

 direction of the strike of the 'Keis Beds, and the foliation and planes 

 of schistosity of the two rocks are parallel. 



" On Grenaat's Kop there is an iiilier of 'Keis Beds surrounded by the 

 Dwyka conglomerate, and a comparatively narrow dyke of "granite 

 traverses the inlier in a direction at right angles to the strike of the 

 latter. The Grenaat's Kop dyke is the only clear case of intrusion of 

 the granite in the 'Keis Series seen in the district. In other parts 

 the contact of the igneous and sedimentary rocks has not been seen, 

 owing to the thick covering of sand, and it would be possible to account 



^ It would seem probable that the later granitic intrusions were due to these same 

 earth-movements . 



- " The Geology of the South-Western Transvaal," by Geo. G. Holmes: Trans. 

 Geol. Soc. S.A., 1906, vol. ix, p. 95. 



^ The Geology of South Africa, by A. W. Rogers, 1905 (Longmans, Green, & Co., 

 London), p. 67. 



•* The geological horizon of these beds is above the !Namaqualaud schists, from 

 wliich they are probably separated by an unconformity. 



