E. H. L. Schwarz — Plains in Cape Colony. 191 



deeply cut into by kloofs and river gorges, but on the north, 

 the great falls of the Orange river at Augrabies interposes a 

 bar of resistant granite to the downward sawing of the river. 

 As a consequence, behind the falls there are extensive plains, 

 the rivers are low grade and when they do happen to have 

 water in them, which is not often, the water spreads out into 

 great kolks and floors some of which are 300 and 400 square 

 miles in extent, for instance, Yerneuk Pan. In one place on 

 the southward side of the main watershed, north of Willow- 

 more, an effective bar is produced by the rivers being deflected 

 along the strike of the beds ; where the neighboring rivers, ex- 

 actly similar in fall and' volume, strike the mountains at right 

 angles, they have sawn through them with apparently no diffi- 

 culty, but in this particular spot the rivers run parallel to the 

 strike of the same mountains, the erosion has been insufficient 

 to allow the rivers behind to cut downwards and a temporary 

 peneplain has resulted.* 



(5) Plains of marine erosion are seldom more than ledges, 

 and I would suggest that in order to keep the two forms dis- 

 tinct they should not be referred to as plains. They are cut 

 by the surf, which undermines the cliffs, and by the off-shore 

 currents which drag the debris backwards and forwards. Gen- 

 erally, however, they may be said to be formed between wind 

 and water, i. e. between high and low waters. "Where the 

 rock is soft, for instance in the case of the Upper Cretaceous 

 deposits of Eastern Pondoland, the ledge is so rapidly cut and 

 extends so far that the outermost edge is only exposed at 

 extremely low tide. This case has puzzled me as to whether 

 erosion has gone on below the general low-water mark or 

 whether the submergence is due to slight sinking; remember- 

 ing, however, the recent sea-beaches round Port Elizabeth 

 elevated only 10 feet or so above high-water mark, showing 

 recent emergence, I am inclined to include off-shore currents 

 as effective in denudation in exceptional cases and where the 

 rock is soft. In regard to the submarine plains such as those 

 on which the Maldive Islands stand, I cannot agree with Stan- 

 ley Gardiner* that they can have been formed by submarine 

 erosion. Soundings in many places showed that the surface 

 had been swept by currents clear of all deposit, but as this is 

 only composed of soft muds, the shells of foraminifera and 

 such like, even on dry land it would have very little effect in 

 wasting rocks harder than itself. In hard rock such as we 

 mostly find on our coast line, the process of cutting shelves is 

 a slow one and the resulting ledge when elevated above the 

 sea is a correspondingly narrow one. 



* Schwarz, E. H. L. , Geological Survey of parts of Prince Albert, Willow- 

 more and Uniondale, Ann. Rept. Geol. Cornni., p. 97 ; Capetown, 1904 ; see 

 also Geographical Journal, p. 272, 1906. 



