190 



E. II L. Schwars — Plains in Cape Colony. 



same elevation. In the long narrow valleys between the moun- 

 tains the character of the plains becomes that of a double bevel — 

 clearly a plain of river erosion (fig. 47), so that we must in this 

 instance distinguish between a plain of marine erosion, a plain 

 of river erosion and one which has been of so general a nature 

 that it includes both. A surf-cut shelf will naturally be a little 

 below that of a river eroded plain, but with long base-levelling, 

 both will so nearly approach the same plane that they will 

 become indistinguishable if only moderately old. I have 

 loosely referred to these great plains as peneplains, and if we can 



Fig. 4. Bird's-eye view of the northern half of the double level in the 

 Kamnianassie River, Oudtshoorn, Cape Colony. The 4000-foot plateau 

 which opens out towards the sea and becomes a plain of marine denudation, 

 in the narrow valleys between the mountains becomes a double level of 

 (river) erosion. The river which runs parallel to the Olifants has reached 

 the same temporary base level at a much slower rate, owing to the more 

 resistant rocks traversed, and hence no alluvial plains have formed along its 

 course. 



include a marginal zone of marine denudation the term will 

 stand, but I am rather inclined to think that writers have always 

 excluded marine denudation from their definition, and in such 

 case we must either coin a new word, such as arch plain, or 

 refer to them simply as plains of denudation. 



(4) Peneplains or plains of river erosion have been suffi- 

 ciently described by Tarr, Davis and others. Temporary pene- 

 plains may be formed by the barring of rivers. Of these we 

 have many excellent examples in South Africa. On the south- 

 ward side of the main watershed the country is everywhere 



