86 PR0E. E. H. L. SCHWARZ ON THE COAST-LEDGES [Feb. 1906, 



height of wall will impound an enormous quantity of water ; in 

 South Africa, big dams are almost out of the question, because 

 the grade of the rivers is so great that, in order to impound any 

 quantity of water, the dam-wall requires to be built so high that the 

 pressure on the base becomes greater than can be safely undertaken, 

 unless at enormous cost. In Europe, the land having gone on 

 sinking for many ages, the rivers have been constantly checked and 

 the downward erosion stayed ; in South Africa, the uplift has been 

 so continuous that the rivers have been converted into agents that 

 sawed downwards, and have often found the rate of uplift beyond 

 their powers of erosion, so that waterfalls along their courses have 

 resulted. 



This remarkable contrast of the two continental surfaces — the one, 

 the European, very old ; the other, the South African, very young — 

 is so striking and so certain, that the relative positions of each of 

 them in the oscillation of land-surfaces, which I have sketched 

 above, cannot be doubted. By establishing the term absolute 

 base-level of erosion, I have endeavoured to give some quanti- 

 tative expression to .a fact which otherwise is difficult to grasp. 



There are many problems that will yield to treatment by this 

 touchstone, such as the tilting of continents, the African north- 

 wards, the European westwards, the American eastwards ; but in 

 South Africa, one has no opportunity of getting together literature 

 on world-wide questions, and I must conclude with the facts as I 

 have observed them locally, and leave to others the task of testing 

 them and applying them to other regions. 



Discussion. 



The President welcomed the first communication read to this 

 Society by one of that enthusiastic band of geologists, the value of 

 whose work had been recently judged on the spot by the members 

 of the British Association who had visited South Africa. He 

 (the speaker) regarded the checking of the results obtained by 

 study of the geology, by reference to the present conditions of 

 non- change, as a matter of great importance. 



Prof. Hull said that he entirely agreed with the Author, that 

 these terraces were the outcome of marine erosion, while the gorges 

 by which they were intersected were due to river-action. The two 

 forms of erosion were here displayed in striking contrast. The 

 occurrence of the marine shells on the 150-to-200-foot shelf was clear 

 evidence, so far as regarded the Bamboes-Bay shelf ; but the evidence 

 of marine sculpturing could not be limited by this occurrence, 

 which must be extended to the remarkably-uniform terrace of the 

 ' Uplands,' if not to those above. The submerged Agulhas Bank 

 was of especial interest, and (in the speaker's opinion) was probably 

 the representative of the great 'continental shelf,' or platform, on 

 which the continents of Europe and Africa were planted, and through 

 which the sub-oceanic river-valley had been cut down for several 

 thousand feet. The speaker thought that the paper was well 



