C. B. Honcood 8f A. Wade— The Old Granites of Africa. 499 



spotted and altered rocks described by Molengraaff, and he considered 

 them as typical hornfels due to the contact action of the granite ". 



I notice that Mr. Jorissen^ in dealing with the Vi'edefort occurrence 

 shows the granite intrusive in certain schists, but does not prove that 

 here it is not also intrusive in the overlying beds, and does not attempt 

 to dispute Dr. Molengraaff's statement of the contact-metamorphism 

 of the Hospital Hill Slates, or to criticize his explanation of the cause 

 of the over-tilting of the strata in this district. 



In March, 1906, Mr. H. Kynaston, Director of the Geological Survey 

 of the Transvaal, in a paper entitled ' ' The Geology of the Neighbourhood 

 of Komati Poort ",- states that in the Old Granite intrusions of igneous 

 rock occur, the majority of which may be classed as dolerites, in the 

 sense in which Teall employs the term, and that they are usually in 

 a well-preserved condition, and constitute a distinct group from the 

 far older basic intrusions, usually referred to as diabases, so common 

 in some of the other formations, such as the Pretoria Series. He says 

 they must be referred to the final stages of the period of volcanic 

 action which marked the close of Karroo times. 



In his paper of the following year, " The Marginal Phenomena and 

 Geological Relations of the Granite north of Johannesburg," he says^ — 



" An interesting modification is found along the slopes of the north 

 face of the Rand between Orange Grove and Bedford. This is the 

 only locality along the Rand, so far as I am aware, where an actual 

 contact can be seen between the granite and the base of the Lower 

 Witwatersrand Series. In one or two other localities further west the 

 granite, or rather its dioritic modification, can be seen within a few 

 yards of the basement quartzites, but in the section between Orange 

 Grove and Bedford we have a clear and well-defined contact exposed 

 for a distance of about a quarter of a mile. 



" This contact is perhaps best seen a short distance west of the 

 western boundary fence of Bedford Farm, and I J miles east 

 of Orange Grove. The normal coarse acid type of the granite 

 crops out on the lower slopes of the escarpment, but within 2 or 

 3 yards of the contact it gradually assumes a foliated structure, 

 which becomes more and more marked up to the actual contact, where 

 the uppermost few inches of the granite are usually in a highly 

 schistose condition. The line of junction is remarkably sharp, and the 

 base of the quartzite pi'esents a well-defined and smooth under-surface 

 resting at an angle of about 35 degrees ixpon the granite. There is 

 not the slightest indication of any intrusive behaviour on the part of 

 the granite, such as characterizes its relation to the basic schists and 

 the older sediments of the Moodies Series. There are no signs of any 

 intrusive veins or pegmatites in the quartzite, or of the granite breaking 

 across from one horizon to another. The whole appearance of the 

 section is that- of a younger series of sediments resting upon an older 

 mass 0? granite. Moreover, the lowest few inches of the quartzite 



1 " Notes on some Intrusive Granites in the Transvaal, the Orange Eiver Colony, 

 and in Swaziland," by E. Jorissen : Trans. Geol. Soc. S.A., vol. vii, pt. iii, 

 pp. 156, 157. 



2 Trans. Geol. Soc. S.A., vol. ix, 1906, p. 28. 



3 Trans. Geol. Soc. S.A., vol. x, 1907, pp. 51-61. 



