Notes on the Becent Limestones of Cape Colony. 431 



As regards the origin of the limestone, its contents point to its 

 having been formed on land, while the form and manner of occur- 

 rence of the more prominent areas make it probable that they are 

 consolidated sand dunes. 



A sample of the stone from Saldanha Bay, used in the new post- 

 office building, Cape Town, was analysed by Mr. Watermeyer,. 

 and found to consist of — 



Carbonate of Lime . . . . . . . . 85-32 



,, Iron .. .. .. .. 1*69 



Silica 12-96 



99-98 



This is the only analysis known to us, but the composition certainly 

 varies considerably owing to the presence of a greater or less amount 

 of quartz sand. 



The shifting sand-dunes along the coast afford good opportunities 

 for comparison. In these dunes the formation of false bedding is 

 often seen in progress, and may be explained somehow as follows : 

 Wind of a certain velocity carries sand grains of a certain weight ; 

 if it increases the sand grains will be heavier, if it diminishes these 

 will be lighter. On a growing sand-dune, where the wind is 

 depositing its burden, the succeeding layers of grains will vary 

 slightly in character as the wind varies in velocity, and in this way 

 distinct bedding is produced. The sand is usually deposited on a 

 slope, and when the wind changes in direction the new layers 

 consequently form at an angle to the older ones, and false-bedding 

 results. 



The alternating layers of slightly different particles offering various 

 resistances to the wind cause the structure of the dune to show up 

 well in places where a section through the dune is being cut, owing 

 to a change in the force or direction of the wind. In the sand- 

 dunes bones and skulls of various land animals are also found 

 accompanied by fragments of marine shells blown up from the beach. 

 If such a range of sandhills as that which lies just above the shore 

 from Cape Agulhas to Cupido's Kraal, were hardened by the 

 deposition of carbonate of lime within it, the result would be a range 

 of limestone hills very like the Bredasdorp one. 



In sheltered spots amongst the sandhills the surface is hardened 

 in this manner, and the same is the case to a lesser extent on some 

 slopes of the dunes themselves. 



The sand-dunes are composed of grains of quartz and other 

 minerals derived from the disintegration of the land, mixed with 



