382 W. M. DAVIS OBSERVATIONS IN SOUTH AFRICA 



sions, and more particularly to Mr Arthur W. Kogers, geologist of Cape 

 Colony; Mr William Anderson, geologist of Natal; Dr G. A. F. Molen- 

 graaff, formerly geologist of the South African Bepublic, and Dr F. H. 

 Hatch, president of the Geological Society of South xAfrica. Our in- 

 debtedness to the first and last named of these accomplished investigators 

 is the greater because of their service in the preparation of admirable 

 handbooks on the geology of South Africa, recently published. From 

 first to last, the generous policy of the British Association, which enabled 

 its foreign guests to take part in the great excursion, awakened our live- 

 liest gratitude. 



The Cape Colony Eanges 

 location and structure 



The southern border of Africa, for a width of from 60 to 80 miles, is 

 a mountainous tract of subparallel ranges extending east and west with 

 much regularity. Singularly enough there appears to be no general 

 designation in common use for this system of mountains as a whole, and 

 I shall here refer to them under the convenient name given above. They 

 are intimately associated, as has already been pointed out, with ranges of 

 less extent running north and south in the southwestern corner of the 

 continent, and they appear to be genetically associated, although not 

 visibly connected with other north and south ridges of less pronounced 

 deformation and relief along the east coast in Natal. The angle where 

 the southern ranges and those of Natal would meet (see figure 1) lies in 

 the Indian ocean, whose shoreline passes obliquely northeast across the 

 series of east-west ranges, the Mesozoic basin of horizontal strata, and tbc 

 series of north-south ranges in the most unconformable fashion, highly 

 suggestive of the truncation of the continent by deformations which have 

 brought the ocean against a new coastline, as will be more fully consid- 

 ered in a later section. 



The strata involved in the Cape Colony ranges are mostly of Paleozoic 

 age, and were originally spread out in great sheets of considerable uni- 

 formity horizontally, but of marked diversity vertically. They constitute 

 the Cape system and the Karroo system. The first system includes the 

 heavy Table Mountain sandstones, 4,000 or 5,000 feet thick; the Bokke- 

 veld (goat pasture) shales and sandstones, containing marine Devonian 

 fossils, about 2,500 feet thick, and the Witteberg series, chiefly sand- 

 stones and quartzites, 2,500 feet thick, or 10,000 feet in all. The Karroo 

 system begins with the extraordinary Dwyka glacial formation, 1,000 

 feet in thickness, after which come the Ecca, Beaufort, and Stormberg 



