80 E. H. L. SCHWARZ 
dolerite area in Fraserburg, and one of them furnishes an illustra- 
tion appearing in Dr. Rogers’ Geology of Cape Colony,* but the 
contacts are covered. In Burghersdorp, Cradock, and in Cathcart, 
at Turnstream, along the Great Kei River, there are admirable 
examples, but only the tops of the great domes appear and no 
estimate as to the size or shape can be arrived at. A very fine one 
occurs on the Kentani coast,’ also exposed only along the extreme 
top, while the enormous ones of Mount Ayliff, Mount Currie, and 
others on the Drakensburg Plateau occur in the Molteno Beds and 
are doubtfully to be ascribed to the same system as the Karroo 
dolerites. The Quizzyhota laccolite, out of all I have seen in 
seventeen years’ traveling in South Africa, is the best for the 
purpose I have in hand. 
Wherever one finds Karroo sediments, especially those above 
the Pareiasaurus zone, there is usually intrusive dolerite. Again, 
where the Karroo sediments have been peeled off and the underlying 
Archaean or Cape system floor is exhibited, there are exceedingly 
few dykes and those that exist are puny, insignificant stringers as 
compared to the massive dykes and sills of the Karroo Beds which 
once lay above them. There is a good example of this to the east 
and west of Prieska. On the east a loop of the Orange River 
incloses a peninsula of Karroo shales with a great sill of dolerite. 
On the west the Griquatown (Pretoria) Beds form the Doornberg 
Hills, through which runs Prieska’s Poort and Keikam’s Poort. In 
both of these gorges thin, nearly vertical, dykes occur, but the 
main portion of the range is quite devoid of dolerite; yet, looking, 
to the south whére the escarpment of the Karroo Beds begins 
practically a third of the height of the hills is occupied by dolerite. 
The occurrence of the dolerite-containing Karroo sediments to the 
west and south of the Doornberg proves that they were once 
continuous over the hills. 
The question remains: Where did the dolerite come from if 
there are such feeble channels of supply in the older rocks? Did 
the Karroo sediments spontaneously melt? I shall seek to prove 
t rst ed., 279; 2d ed., 286. 
2 E. H. L. Schwarz, “Origin of the Rand Bankets,”’ Journal Assoc. for Advance- 
ment of Science, S. Africa, VIIL (Cape Town, 1012). 
