76 PKOF. E. H. L. SCHWARZ ON THE COAST-LEDGES [Feb. I906, 



In Bredasdorp and Biversdale there is an immense accumulation 

 of blown sand on the coast. The dunes rise to 600 and 800 feet 

 above sea-level, and rest upon shelves of varying heights. In 

 Bredasdorp, near Cape Infanta, the base is seen some 100 feet 

 above sea-level, and is composed of hard quartzites ; to the west, 

 however, the base goes below sea-level. 1 In Biversdale the base 

 seems to have been generally only a few feet above sea-level, and 

 the strata consist of exactly the same rocks as those which go to 

 form the ruggens- country behind — namely, Bokkeveld Slates. 



Sand on the southern coast of South Africa is shell-sand. The 

 waves throw up the valves of dead molluscs, which get rolled up and 

 down by the ebb and flow of the tide, and finally are broken into 

 such small fragments that the wind can carry them away. This 

 sand, then, masses up in these great dunes, sections of which show 

 very clearly that the whole of the deposit is wind-borne ; for the 

 false bedding is so abrupt and striking, that no streams or currents 

 could have produced such marked effects. The angular fragments of 

 shells sometimes break down to a powdery, chalky mass ; but as a 

 rule the sand remains just as it was, piled up without any alteration 

 except on the surface. Where rain-water can penetrate and come 

 to rest, there is a process of solution and redeposition of lime 

 which consolidates the sand into a rock hard enough to be used for 

 building-purposes. 



The fossils found in the sand-dunes are all of recent age, the 

 commonest being the snail, Cyclostoma, In the two districts with 

 which we are immediately concerned, bones of the elephant, 

 rhinoceros, eland, sable antelope, and large carnivores have been 

 found — all species which have, since the coming of the white man, 

 disappeared from this neighbourhood. 



In Biversdale and Bredasdorp the level of the top of the sand- 

 dunes is very nearly the same as that of the plateau behind ; there 

 has been a little erosion at the junction, and a well-watered valley 

 extends at the inner foot of the dunes ; the rise, however, from 

 the old high-level plateau to the dune-country is very slight. In 

 George and Ivnysna there is a very similar accumulation of sand ; 

 only here the original bluff of the plateau, rising steeply in preci- 

 pices from sea-level to 600 feet, is bare, and between it and the 

 sand-dunes there is a level tract of low country occupied by the 

 far-famed Knysna Lakes. I should be inclined to atttribute the 

 difference between the tw r o tracts to the direction of the prevailing 

 winds. In Biversdale and Bredasdorp this would have been 

 slanting with respect to the land, whereas in Knysna the winds 

 blew straight from the sea. In the latter case the steep cliffs would 

 have produced a back-eddy which swept the sand away from their 

 base, whereas in the former the sand could be piled up against 

 them. Whatever be the explanation, the difference does exist. 



1 See Rogers & Schwa rz, 'Notes on the Recent Limestones on Parts of the 

 South & West Coasts of Cape Colony ' Trans. Phil. Soc. S. A. vol. x (1897-98) 

 p. 427. 



