2 DRAINAGE SYSTEMS 



feature about eighty miles north of Calvinia, bring the 

 level of the surface down from some 5,000 feet to 500 

 feet above the sea. South of the Bokkeveld Mountain 

 (an important escarpment west of Calvinia which must 

 not be confused with the mountains of the Cold Bokke- 

 veld in Ceres) the Cederberg chain commences, and 

 forms, together with its subsidiary parallel ranges, a 

 broad belt of mountainous country rising to the height 

 of 6,000 feet between the Karroo and the coastal district. 

 The southern drainage slope is also very different in 

 the west and east. In the west there is a sharp drop 

 immediately south of the watershed, and the Great 

 Karroo lies between it and the Zwartebergen, which rise 

 to a height of over 7,000 feet above the sea, and some 

 5,000 feet above the Karroo. The Zwartebergen, Lange- 

 bergen, and the minor ranges parallel to them, run 

 nearly east and west, together forming a wide tract of 

 mountainous country which stretches from Tulbagh to 

 the Indian Ocean east of Grahamstown. This belt is 

 traversed by the rivers flowing from the Karroo, gener- 

 ally in deep, steep-sided valleys, which become gorges 

 in the mountain ranges. There are many longitudinal 

 valleys in this region much more open and less steeply 

 graded than those of the transverse rivers into which 

 their waters flow. The country between the Zwarte- 

 bergen and Langebergen, occupied by longitudinal val- 

 leys, lies somewhat lower on the average than the Great 

 Karroo. South of the Langebergen the surface slopes 

 towards the coast, but it is deeply cut into by rivers, and 

 diversified by mountains such as Aasvogel Berg, Pot 

 Berg, and the mountains of Caledon and Bredasdorp. 



