80 PIU)F. E. H. L. SCHWARZ ON THE COAST-LEDGES [Feb. I906, 



and this I will shortly describe. Thus our sub-continent seems to 

 have been subject to lifts of 600 to 700 feet or so, with smaller 

 intermediary halts and set-backs. 



Shell-sand, green sand, mud, and boulders have been dredged 

 off the surface of this submarine plateau. For some years now 

 the s.s. Pieter Faure, the Government trawler, has been making 

 investigations over this area with regard to the supply of fish ; 

 and when the records are worked up we shall have, perhaps, some 

 more definite data upon which to go. Some large quartzite-boulders, 

 dredged 40 miles off Mossel Bay, showed that there at least land 

 must have been at one time. The occurrence of this plateau, 

 corresponding so closely with that which surrounds the eastern 

 shores of America and the western shores of Europe, led me, in 

 a recent paper, to suggest that it was caused by the bending of the 

 edge of the continent seawards : owing to the carrying-away of 

 material from the interior by denudation, and consequent relief 

 of weight, and the deposition of this material as sediment off the 

 shores, and consequent weighting of this area. If, however, we 

 consider the coast-ledges to be plains of marine denudation, this 

 explanation is unnecessary, as we have evidence of block-uplift 

 of the whole continent, and not of bending of only small portions 

 of it. 



Whether there are plateaux below the Agulhas Bank, must 

 remain problematical, until more extensive exploration and sound- 

 ings have been made. The evidence, so far as we now can judge, 

 goes to suggest that the ground off the Bank belongs to the 

 absolute base-level of erosion — that level beyond and 

 below which the action of running water was never 

 effective, taking the continent as the unit which it now is. In 

 former ages there may have been elevations and depressions along 

 the coast which had an absolute base-level different from that 

 which we assign to the movement that we see going on at the 

 present time : an elevation, for instance, that may have connected 

 the island of Madagascar with the mainland, or a depression 

 that permitted the deposition of the Cretaceous marine rocks or 

 the Karroo Beds. These periods are, however, remote, and our 

 powers of reconstructing the physical conditions of the continent 

 are faulty, from the want of data upon which to go ; consequently, 

 we are not likely to have more than one absolute base-level at 

 any one place to deal with, and the confusion of speaking of 

 several absolute base-levels will be avoided. There is a change in 

 the fauna exhibited in the 200-foot shell-deposits at Port Elizabeth 

 and Uitenhage ; and if the 2500-foot plateau had remains of 

 animal life upon it, they would indicate a further change, but there 

 is nothing to lead one to suppose that even the highest undoubted 

 surf-cut shelf was made in times as far back as the Tertiary. 



The absolute base-level of erosion, as I conceive it, 

 refers simply and solely to the movements of con- 

 tinents as they now are, and has nothing whatever to do 



