PHYSIOGRAPHIC DIVISIONS 381 



climate for the next inland lowlands of erosion. The broadest of these 

 is known as the Great Karroo, and lies between the northernmost moun- 

 tain ridge and the south-facing escarpment of the interior highland, while 

 a similarly arid belt between two of the chief mountain ridges is called the 

 Little Karroo. In distinction to these lower areas, the highland of the 

 Veld, next north, is sometimes called the Upper Karroo. 



The descent of the interior highland on the east to the coast of the 

 Indian ocean is relatively rapid. Here the rainfall from the impinging 

 trade winds is more plentiful and vegetation is more luxuriant. The 

 streams of this slope have a pronounced gradient and are actively en- 

 croaching on the headwaters of the Orange Eiver system by which the 

 highland is drained to the Atlantic. The western side of the highland is 

 more arid and includes the desert of Kalahari, of which we saw only the 

 eastern margin on our northward journey. 



PROBLEMS HERE CONSIDERED 



The opportunity for geological and geographical study during a land 

 journey of only 33 days, during which a distance of about 2,500 miles 

 was traversed by rail, was distinctly limited. Nevertheless, by taking- 

 advantage of as many geological excursions as possible and by devoting 

 close attention to the study of the landscape during the train journeys, 

 much profit was derived, no small share of which came from the very 

 advantageous conferences with South African and European members of 

 the party. The chief subjects here presented are: The Cape Colony 

 ranges, considered with special regard to their resemblance to the Alle- 

 gheny mountains of Pennsylvania and Virginia; the Dwyka (Permian) 

 glacial formation, or tillite, to which more attention was given on the 

 ground than to any other problem; and the peneplain of the Veld or 

 interior highland and the conditions of its origin. Briefer discussion 

 is made of the origin of the zigzag gorge below the Victoria falls of the 

 Zambesi, in which the explanation offered by Molyneux is accepted, and 

 of several general problems, such as the continental origin of the Karroo 

 and other formations; the homology of the Karroo Mesozoic basin with 

 the Tarim basin of central Asia, the probability of the former greater 

 extension of Africa to the east, south, and west, and the dissimilarity of 

 South Africa and southern South America. 



A CKN O WLED GMENTS 



Special acknowledgment of assistance is due to all the South African 

 geologists who gave us the aid of their experience on the various excur- 



