78 PROF. E. H. L. SCHWAEZ ON THE COAST-LEDGES [Feb. I906, 



water to come to rest on, and explaining at the same time how it 

 is that loose sand is not similarly consolidated. At Port Elizabeth 

 there is a beach- deposit cemented into what is known in South 

 America as a stone-reef : this may have been formed in situ, 

 for the sea-water, when the tide ebbs, would be retained under 

 the rounded stones, and carbonate of lime deposited as the water 

 became heated. 



At Hermanuspetrusfontein, on the Caledon coast, there is a well- 

 marked surf-cut ledge about 50 feet above sea-level, 1 which would 

 correspond to the ledge of rock underlying the sand-dunes at Cape 

 Infanta ; while farther out, at Danger Point, the sand-dunes rest 

 upon a ledge that has sunk beneath the sea. At Agulhas Point the 

 Jedge is just at sea-level round the lighthouse, but it is very narrow 

 here. Most of these places along the coast are so inaccessible, and 

 the problems with which we are concerned in this paper have 

 been so recently advanced, that the exact heights of any one of 

 these ledges has not been determined with any accuracy ; but the 

 point which I wish to bring out is that there are more or 

 less extensive ledges, admittedly surf-cut, at various 

 levels above and below tide-mark along this part of 

 the coast. 



The Cape Peninsula extends from Cape Point to Table Bay, and is 

 a precipitous mass of sandstone resting upon a basement of pre-Cape 

 rocks and granite. It is separated from the mainland by a wide 

 tract of low-lying country covered with drifting sand, known as the 

 Cape Flats. The sand is gradually being fixed by plantations 

 of trees, and quickgrass and other creeping plants, but much of it is 

 still pure, loose sand. If one bores through the sand one meets first 

 with a layer of ironstone-gravel (the so-called laterite), and then 

 a thickness of clayey material derived from the weathering of the 

 Malmesbury Beds, and finally the hard blue clay-slate itself. It is 

 very difficult to say at what level the true rock-shelf exists under 

 the sand, owing to the want of available evidence ; but I think that 

 the ironstone may be said to rest upon the original surface. This, 

 then, is commonly found near sea-level, taking an average, sometimes 

 going below, sometimes occurring above that datum. Geologists have 

 always been very chary in expressing an opinion as to the nature of 

 the cause which cut this level fiat ; but I see no reason for propound- 

 ing a separate explanation for this particular plain, when we have 

 similar ones, clearly surf-cut, all along the coast to the east. The 

 laterite-, gravel-, and lignite-deposits seem to point to these having 

 been formed on land, but the shingle and tree-trunks may have been 

 rolled to their places by the sea, and the laterite can and does form 

 in situ beneath any sandy soil. Therefore I see no hindrance, in the 

 nature of the deposits found in the Cape Plats, to the acceptance of 

 the agency of sea-waves in cutting the original plain. There need 

 not here be any question of a strict mathematical plane : for we 



1 A. W. Eogers, ' The Geology of Cape Colony ' 1905, p. 380. 



