Page:South African Geology - Schwarz - 1912.djvu/101

 symmetrical point. Its farthermost edge is 90 fathoms, and beyond that is very deep water. Boulders have been dredged from oft it 40 ml. from land, consequently this shelf was once dry land. Further evidence of this sinking is furnished by the rivers, such as the Buffalo at East London, where the rock channel lies 122 ft. below sea level, the shallow channel now existing being due to the filling in of the rock channel with sand.

All these levels mentioned are major stages; each has an indefinite number of minor stages. Looking from the Cockscomb Mountain over the country about Port Elizabeth one sees the land cut into a succession of steps down from the 4000-ft. level. In the case of the 1500-ft. level in this area the marine deposits (Alexandria Beds) occur on every level with similar shells down to that forming on the present shore, showing that the land rose by stages of 50 to 100 ft. at a time, then rested, allowing a shelf to be cut, and then rose again, and so on. The steps in such a case belong to one and the same plain, like the steps of a staircase belonging to one flight of stairs, and such a stepped plain is called a klimakotopedion, which is simply the English term translated into Greek. The submerged Agulhas plateau is of the same nature, as has been shown by soundings. Inland, the major stages are similarly stepped, owing, in this case, to rivers being checked at various levels. Thus at Grahamstown the high hills around belong to the 2500-ft. level, the flats about the town are some 250 ft. lower, and the town itself is in a V-shaped river valley not old enough to have been levelled. The levels run throughout South Africa with extraordinary constancy. Local variations occur, causing any particular level to be above or below the normal. This is due to the presence or absence of