C. B. Honvood S^ A. Wade— The Old Granites of Africa. 463 



Afjaiu, he describes the granite of Paarl Mountain as a biotite 

 granite associated with dykes of quartz - porphyry but not with 

 gneiss. Further, he remarks that " the granites of the Paarl and 

 Stellenbosch districts contain a fair amount of microcline, a variety 

 of felspar which is rare in the Saldanha Bay and Darling area, 

 although it seems to be the chief felspathic constituent of the granites 

 in the northei'n and north-western parts of the Colony. On the south- 

 west edge of the JSottelary granite cassiterite or tin-stone occurs in 

 a gneissose mnscovite granite, together with tourmaline ; wolframite 

 has been found in the same neighbourhood ". 



In describing the smaller of the two granite masses near Somerset 

 West, he says: "The main mass of the intrusion is a biotite granite 

 with little mnscovite, but the muscovite is very abundant in certain 

 places and the felspar decreases in amount and may disappear 

 completely, so that the rock becomes a greisen or quartz-muscovite 

 rock. In other parts tourmaline is extremely abundant, sometimes 

 giving rise to a schorl rock, composed of tourmaline and quartz only. 

 At other places andalusite, showing a beautiful pink tint under the 

 microscope, forms a large part of a rock composed of quartz, 

 tourmaline, muscovite, andalusite, and apatite." 



Professor E. Cohen,' of Greifswald, has recorded the presence of 

 pinite (an alteration product of cordierite) in the biotite granite of 

 Table Mountain. Mr. Rogers ^ de.scribes the granite mass of George 

 as containing both muscovite and biotite granites, with tourmaline and 

 fluorspar ; and associated with gneissose rocks. 



With regard to the granite and gneiss of the Prieska district, he ^ 

 observes that the foliation planes of the gneiss are in general parallel 

 to the strike of the sedimentarj- rocks in its neif^hbourhood ; he 

 thinks it not unlikely that the intrusion and solidification of the 

 granite and gneiss occupied a long period, and that we have in 

 the gneiss the earlier, and consequently most altered, products of 

 the acid magma; but he says that " whether any part of the granite 

 is of much later date than the bulk of the intrusions is not yet 

 settled. Some of the very fresh -looking granites on the farm 

 Schalk's Puts might certainly be considered younger than the gneiss, 

 but there are so many intermediate varieties that the evidence of 

 a considerable difference in age between the extreme types must be 

 clearly made out before that opinion can be accepted ". He then 

 proceeds — 



" The chief constituents of the acid intrusions are quartz, 

 orthoclase, microcline, albite, and an intergrowth of orthoclase or 

 microcline, and a plagioclase felspar, black and white mica, the 

 latter sometimes (e.g. Grenaat's Kop and Alicedale) in crystals up to 

 10 inches in width, but too frequently bent by the movements which 

 the rock has undergone since its solidification ; hornblende is not 

 often met with ; apatite and iron ores are not abundant ; garnets 

 occur, especially in certain gneisses, and in the rocks with the same 



' " Geognostisch-petrographische Skizzen aus Slid Afrika : " J^'eues Jahrbuch 

 fiir Min., etc., 1874, p. 460. 



^ The Geoloqy of Cape Colony, by A. W. Rogers, p. 44. 

 ^ Loc. cit.,"pp. 79-83. 



