C. B. Honvood S^ A. Wade— The Old Granites of Africa. 459 



1 . Origin. 



2. Ao-e. 



Chief 



Macroscopical 



Characteristic. 



Chief 



Microscopical 



Characteristic. 



Chief Fiehl 



Characteristics. 



4. 



Old Graniies. 

 Plutonic. 



Primary or fundamental. 



Usually of a grey colour. 



New Granites. 



Volcanic (inasmuch as 

 it represents the intra- 

 liquid slowly - cooled 

 portion of an enormous 

 volcanic sheet). ^ 



Later than the Pretoria 

 Series, probably later 

 than the Waterberg 

 Series.^ 



Red in colour. 



Very general presence 

 of microcline. 



Presence of quartz and 

 pegmatite veins and 

 diabase dykes. Mar- 

 ginal modifications ; 

 such as quartz-diorite, 

 schists, and gneissic 

 granite ; association 

 with amphibolite rocks, 

 schists, and gneisses. 



Very general presence of 

 granophyric structure. 



Association of three 

 types— 



1. Upper felsitic 

 portion. 



2. Hypidiomorphic 

 granite, originally 

 intermediately situ- 

 ated. 



3. Panidiomorphic 

 granite, originally 

 centrally seated, or 

 interior. 



Also presence of more 

 basic rocks around its 

 periphery, such as sye- 

 nites, norites, gabbros, 

 pyroxenites, etc. 



Possibly some slight latitude must be allowed in this use of the 

 term volcanic, to give greater antithesis to the above comparison of 

 the two granites. It designates rocks which have consolidated at or 

 near the surface,^ and it is in this latter sense that it is here employed. 



Dr. Molengraaff says:* "I consider the Red Granite, as forming 

 a portion of an enormous sheet, although of a decidedly micro- 

 pegmatitic structure, has much in common with that of the plutonic 

 rocks, which is my justification for still retaining the name Granite. 



1 Geological Survey of the South Afrioau Republic, Annual Report for 1898, by 

 Dr. G. A. F. Molengra.'iff, pp. 5, 6. 



2 Some of the Red Granite is certainly more recent than the Waterberg Series, 

 mde " The Waterberg Sandstone Formation and its Relation to other Formations of 

 the Transvaal", by E. T. Mellor (Trans. Geol. Soc. S.A., 1904, vol. vii, pt. i, 

 p. 45) ; also " The Red Granite of Balmoral and its Relations to the Cobalt Lodes", 

 by C. B. Horwood (Trans. Geol. Soc. S.A., 1904, vol. vii, pt. ii, p. 110). 



3 British Petroqraphti, by J. J. Harris Teall, p. 451. 



« Geol. Surv. of the S.A. Republic, Ann. Rep. for 1898, pp. 5, G. 



