Dr. G. Sandberg — The ' Old Granite^ of the Transmal. 555 



distinctly disowns the well-known most erratic manner in which igneous 

 rock in its unconsolidated state affects adjacent sedimentary strata. 

 Still, I am convinced that he is not ignorant of the fact that eruptive 

 rocks send out intrusive offshoots, sometimes high into the covering 

 sedimentary strata, right into very recent deposits at one place, whilst 

 their action appears hardly perceptible even at their contact with the 

 oldest covering rock at another place. It is also surely not unknown 

 to him that such extreme effects may be situated in immediate vicinity 

 to one another. 



Lastly, may it now be taken as generally recognised that the intensity 

 of the action of the unconsolidated eruptive magma on the sedimentary 

 strata is more or less proportionate to the intensity of the effect of 

 the mountain-folding energy which was brought to bear upon them, 

 and stands in distinct relation to the position of the respective rocks 

 in the tectonic structure thus engendered.^ 



That Dr. Corstorphine should generalise and conclude that the ' old 

 granite ' is not intrusive in the W.W.R. Beds, because over the vast 

 fold granite' area of the Transvaal, the N^orthern Orange Eiver Colony, 

 North-Eastern Cape Colony, and Southern Ehodesia he discovers one 

 single place where over the extent of the exposed contact between this 

 granite and the overlying W.W.R. Beds (200 yards) he is unable to 

 find any evidence of contact-metamorphism, seems rather hazardous 

 and a somewhat premature conclusion. 



Neither the discovery in the "VV.W.E,. quartzites of the rounded 

 bluish quartz-pebbles, of extremely problematic origin, at the contact 

 of the granite and these W. W.R. Beds, nor the determination of the 

 sericite-schists occurring below the Orange Grove quartzites to be 

 segregations of the granite (in spite of the absolute conformability of 

 these schists to the lowest W.W.E,. Beds and the presence of con- 

 glomerates composed of quartz-pebbles- in them), seems to render more 

 satisfactory the conclusions arrived at. J^evertheless, they are eagerly 

 seized upon by Dr. P. H. Hatch and Mr. E. Jorissen to serve as the 

 basis of their arguments for ' proving ' the existence of an Archaean 

 formation older than and unconformable to the W. W.K.. Beds. 



Even supposing that it had already been demonstrated beyond the 

 possibility of a doubt that in the Zoutpansberg district (and Barberton 

 district, etc.) the granite is of the same age as the 'old granite' 

 (of A^'redefort, Johannesburg, and Heidelberg bosses), Dr. Hatch's 

 reasoning must forcibly strike the unbiassed mind as singular. ^ He 

 describes '^ the complex of highly altered crystalline schists at Mount 



' C. G. S. Sandberg- : " Etudes geologiques sur le Massif de la Pierre-ii-voir (Bas 

 Valais)," 129 pages in 8vo, Paris, 1905, pp. 108-10; " L'age du grauit des Alpes 

 occidentales et I'origine des blocs exotiques cristallins des Klippes," C.R. Ac. Sc, 

 1905, t. cxl, pp. 1072, 1073 (10 avr.) ; " L'age du granite Alpiu," Arch. Sc. phys. 

 nat. (4), Geneve, 1907, t. xxiii, pp. 581-94. E. Weiuschenk, " Grundziige der 

 Gesteinskunde," 2 vols., Freib.-i.-Breisgau, 1906. 



^ G. A. F. Molengraaff, discussion on Mr. Jorissen's paper, " Note on some 

 Intrusive Granites, etc.," Proc. Geol. Soc. S. Africa, to accompany vol. vii, p. xxxii. 



^ Dr. G. A. F. Molengraaff : Discussion of above paper, Proc. Geol. Soc. 

 S. Africa, to accompany vol. vii, pp. xxix-xxxi. 



* Dr. F. H. Hatch, " The Oldest Sedimentary Rocks of the Transvaal " : Trans. 

 Geol. Soc.S. Africa, vol. vii, pt. iii, pp. 147-50. 



