70 PEOF. E. H. L. SCHWAKZ ON THE COAST-LEDGES [Feb. I906, 



5. The Coast-Ledges in the South- West of the Cape Colony. By 

 Prof. Ernest H. L. Schwarz, A.K.C.S., F.G.S., tthodes 

 University College, Grahamstown, South Africa. (Read 

 November 8th, 1905.) 



The subject of continental ledges has recently been brought into 

 prominence in Europe and America by Prof . Hull, Prof . J. "W. Spencer, 

 and others ; it is one in which attention to details has revealed 

 many surprising results, which have modified our conception of the 

 relation of land to sea, with the host of cognate problems. I 

 offer the present contribution on the same subject, with the object 

 of further emphasizing the importance of such investigations ; for 

 in South Africa we have the same set of phenomena, although we 

 are able to study the movement in quite a different phase from that 

 in which we find it in Europe and along the eastern coast of North 

 America. 



The writings of the above-mentioned authors, together with 

 those of Prof. J. Geikie, Prof. A. Issel, and Prof. "W. C. Brogger, 

 have made the subject so familiar of recent years, that I need 

 not enter into a discussion of the general principles involved. 

 Suffice it to say that, as the land rises, there are set-backs which 

 allow the wash of the breakers to cut level plateaux of marine 

 denudation ; when a maximum elevation is reached, the land 

 sinks and these ledges or fringing plateaux can be traced in the 

 soundings set down on charts of the coast. In Europe, the first 

 to draw attention to the subject were Godwin-Austen 1 and De la 

 Beche 2 ; and since then, the surveys for the submarine cables have 

 furnished the information for a very complete statement of the 

 occurrence in the North Atlantic. 



In the following pages I will set forth what evidence we have 

 along the southern coast of Cape Colony for the existence of these 

 fringing plateaux, and then at the end compare them with the 

 European and American ledges. 



The most striking of the coastal plateaux is that rising from 

 600 to 800 feet above sea-level, which extends from Caledon to 

 Port Elizabeth. In the west it is cut in Bokkeveld (Devonian) 

 Slates, with here and there inliers of sandstone that rise from the 

 plain in the form of hills. To the eye of a casual traveller there is 

 very little evidence of a plain in this country ; for there is a perfect 

 labyrinth of steep-sided gorges, which cut the land into narrow 

 ridges, or ruggens, as they are called in Dutch. If the observer, 

 however, climbs on to an eminence and looks across the valleys, he 

 notices that all the ridge-tops are cut to a level which slopes gently 



1 'The Valley of the English Channel' Quart. Journ. Geol. Soc. vol. vi 

 (1849) p. 69. 



2 ' Geological Observer' 2nd ed. (1853) pp. 90-91. 



