410 ORIGIN OF VLEIS 



the Transkei and Pondoland very many small streams 

 rarely bring down enough water to break through their 

 sand bars, and in time they will form corresponding 

 alluvial tracts with small channels traversing them. 

 The comparatively recent elevation of the coast that 

 enabled these rivers to cut deep valleys through the 

 coastal plateau has not been of sufficient duration to 

 allow them to silt up their lagoons. 



A vlei is sometimes formed along the course of a river 

 just behind a ridge of rock that is with difficulty cut 

 through by the stream or behind a belt of sand dunes. 

 The softer rock behind the obstruction allows the river 

 to cut out a wide plain, and by the unequal distribution of 

 debris over the plain the bed of the stream may be raised 

 slightly above the level of the plain, causing the latter 

 to be flooded at times. A process of this sort has taken 

 place in the valley of the Bosch Kiver where it ap- 

 proaches the Bokkeveld hills west of Witte Vlakte. An 

 extensive vlei or pan, on the farm named Poortje, is the 

 result, and the river has found an easier course to the 

 south, where it joins the Draai Kraal's Kiver. 



Very extensive "vloers" are formed along the rivers 

 entering the Orange Kiver from the south, and are pro- 

 duced by the spreading out of the river course over a 

 red clay flat. 



The water that gathers in these river vleis is some- 

 times brackish from the salts derived from the soil ; 

 especially is this the case after it has been standing for 

 some time. 



