388 ALLUVIAL DEPOSITS 



gorge, with vertical walls some 600 feet high, in the 

 heart of the mountains. Before entering the gorge the 

 Olifant's Kiver runs for some eighty miles over flat 

 country, and this tract is very rich in alluvium, especially 

 below the junction of the Meiring's Poort stream. Under- 

 lying the alluvium there are rocks belonging to the Uiten- 

 hage group, which are soft and easily eroded compared 

 with the Table Mountain sandstone. The mountains 

 have acted as a check to the downward cutting of the 

 river, that has consequently widened its valley behind 

 them and deposited the alluvium to which the Oudt- 

 shoorn Division owes its wealth. These accumulations 

 are gathered from nearly all the rock systems in the 

 Colony, from the Pre-Cape rocks of the Cango to the 

 Uitenhage beds of their immediate vicinity. The Gamka 

 has formed a similar but smaller alluvial tract between 

 Sand Berg (or Paarde Berg) and the Roode Berg gorge, 

 and others occur lower down its course. 



Another tributary of the Gamka, the Buffel's River, 

 has cut a wide alluvial plain behind the Klein Zwartberg 

 which it enters at Leeuw Kloof Poort. 



Great tracts of alluvium are found along the rivers 

 which flow northwards from the main watershed to the 

 Orange River. The Fish, Rhenoster, and Zak Rivers 

 in Sutherland, Fraserburg, and Calvinia, are especially 

 rich in alluvial deposits derived from the Beaufort beds 

 and the dolerite north of the watershed. Where water 

 can be easily brought on to these lands they are ex- 

 tremely fertile. Tontelbosch Kolk in Calvinia, a farm on 

 the banks of the Rhenoster, is perhaps the finest grain 

 farm in the Colonv. The fall of these tributaries of the 



