T. RUPERT JONES 



[march 



miles), and northward to Mafeking (about 40 miles), as well as its 

 northward range on the east side, have been mapped by other 

 geologists. From the mouths of the Gualana and Breka rivers to 

 St. John's (40 miles) is a blank, this special band there lying on 

 the ocean-bed. From St. John's to Swaziland is about 70 miles. 

 Altogether, the known length of the outcrop of this " Dwyka Con- 

 glomerate " is more than 1000 miles. 



Stretching from one side of this southern part of the continent to 

 the other, with a roughly semicircular contour on its southern line, it 

 encloses a large gulf-like area, less oblong and more crescentic than 

 the Bay of Tripoli on the north African coast, and of somewhat greater 



Outline Map of South Africa, slightly modified from that published by David Draper in 

 Trans. Geol. Soc. S. Africa, 1896, vol. i. 



length. Its further extension at the sides to KW. and N.E., from 

 about lat. 30° S., between the meridians 25° and 33° E. long., prob- 

 ably fails to indicate its real extent. 



The locality where this great boulder-band was first specially 

 noticed was at Ecca Vale and Ecca Heights, near Grahamstown ; and 

 it has been referred to as the Ecca Conglomerate by some writers, but 

 since E. J. Dunn, formerly Colonial Geologist, noticed a good section 

 of this rock, where traversed by the Dwyka river (one of the head- 

 waters of the Gauritz in Cape Colony), it has been called the " Dwyka 

 Conglomerate." 



The constitution of this innermost band of the concentric coast- 

 ranges has been variously described by observers according to its 



