410 W. M. DAVIS OBSERVATIONS IN SOUTH AFRICA 



tion were so closely associated, and for this reason, if for no other, the 

 introduction of the new term "tillite," as suggested by Penck at the Jo- 

 hannesburg meeting of the Geological Section of the Association, seems 

 desirable. 



The general relations of local outcrops at Vereeniging to the older 

 formations as far as Johannesburg are roughly shown in figure 10, drawn 

 with aid from Doctor Hatch. In this connection Hatch's Geological Map 

 of the Transvaal, in Hatch and Corstorphine's book, should be consulted. 

 It is thus seen that the Karroo system, in which the Dwyka and Eeca 

 formations are the lower members, is the latest of five great geological 

 systems separated from one another by unconformities (undulating lines 

 in figure 10). Crystalline rocks, believed to be Archean, form the base 

 of the section north of Johannesburg. On these lie the strata of the Wit- 

 watersrand system, with a lower member including the banded jaspers of 

 the Hospital Hill series, which resemble similar rocks in the region of 



Figure 10. — General Section from Johannesburg to Vereeniging. 



J, Johannesburg; V, Vereeniging; Cr, basal crystalline rocks, exposed north of Jo- 

 hannesburg ; HH, Hospital Hill series, the lower part of the Witwatersrand (W) system, 

 in which the gold-bearing "banket" or puddingstone occurs ; KA, Klipriversberg amyg- 

 daloid, of the Ventersdorp system ; B, Black Reef quartzite, Do, Dolomite, and P, Pre- 

 toria quartzites, these three forming the Pretoria or Potchefstroom system ; Ko, Karroo 

 system, here including the Dwyka tillite and the Ecca shales. 



lake Superior, and an upper member including the famous gold-bearing 

 Banket or "puddingstone" of the Band. Next comes the Ventersdorp 

 system, here chiefly composed of the volcanic rocks of the Klipriversberg 

 amygdaloid. Then follows the several members of the Potchefstroom 

 system (according to the terminology of the authors above cited), first the 

 Black Beef quartzite, here unusually thin and unimportant topographic- 

 ally; then the heavy dolomites, from which the water supply for Jo- 

 hannesburg is largely derived; and last the Pretoria quartzites. The 

 unconformities below and above the Ventersdorp system are not marked 

 by striking differences of dip; the unconformity by which the Karroo 

 system is separated from all the older rocks is much more pronounced. 

 These structural features will be seen to be of importance when the 

 topography of Dwyka time is considered in a later paragraph. 



A mile or two northeast of Vereeniging the Sugarbush branch of the 

 Vaal river opens a short section with Klipriversberg amygdaloid at the 

 base, unconformably covered by Black Beef quartzite and its associated 



