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PHYSICAL GEOGRAPHY OP THE CAPE COLONY. 265 



not above six inches long and well rounded ; but large subaugular 

 blocks were not uncommon. The conglomerate is sometimes very 

 massive and makes fine mural escarpments ; sometimes uncon- 

 solidated, when it weathers into rounded gravelly hills. Lenticular 

 bands of fine sandstone are interbedded with it. The only fossils I 

 heard of from it were bits of carbonized wood : it contains lenticular 

 beds of lignite. It has the character of a lacustrine deposit, formed 

 at a time when the configuration of the country was not very 

 different from what it is at present, but when the valley in which 

 it lies was occupied by a lake. I know of nothing that would give a 

 clue to its age. 



Sv/perficial Deposits. — These are very varied and extensive and 

 offer many points of interest. They have received notice at the 

 hands of sundry geologists ; but, for reasons already given, I have 

 not appended detailed references to previous descriptions. The great 

 plains of the Ecca Beds and Kimberley Shales are often overspread 

 with sheets of red sand, and this frequently contains a considerable 

 quantity of black metallic-looking particles, which I found in one 

 case to be ilmenite. I think there is no doubt that the sand is 

 formed by the decomposition of the Trap sheets and dykes, and 

 spread about by the wind. I have frequently noticed as many as a 

 dozen little whirlwinds careering over the extensive plains at the 

 same time, each one marked by a cloud of sand spinning through 

 the air. 



Great deposits of calcareous tufa are also common on the plains, 

 the material for which, I believe, is furnished by the decomposition 

 of the lime-felspars of the traps. The carbonate of lime, however, 

 is carried far away from the source from which it is derived, and 

 often spread out in extensive sheets. I fancy this has been brought 

 about somewhat in this way : — the violent torrential downpours of 

 rain for which the country is so notorious will in a quarter of an 

 hour convert a parched plain into an almost continuous sheet of 

 water. When the surface-water has run off, the subsoil remains 

 saturated, and the water, percolating about, gradually rises to the 

 surface, is evaporated, and deposits the carbonate of lime it has 

 taken up during its underground journey. 



The Cape Elats are covered with very mixed material ; part of it 

 is obviously decomposed granite ; it also contains a large number of 

 rounded quartz-grains, which may well have come from the Table- 

 Mountain Sandstone ; and part is sand blown in from the coast. 

 The whole seems to have been mixed and distributed by wind. 

 Alongside the rivers this mixture has been arranged in a rudely 

 bedded form, and contains layers of carbonized twigs, branches, and 

 roots, forming a poor kind of lignite. Xear Cape Town there is a 

 good deal of lumpy stuff, called " gravel," and looking not unlike 

 gravel. When one of the lumps is broken it is seen to be composed 

 of quartz- grains cemented by limouite, or of clayey matter stained 

 and bound together by a similar cement. 



At the tenth milestone from Cape Town, on the Maitland road, 

 a very curious boss of rock sticks up through the loose superficial 



aJ.G.S. No. 174. T 



