Physical Composition of Capk Colony .Soils. 



101 



iiig a half-iiicli uiniual ilepusit — iiicioase the prupoition of silt an<l clay 

 in the soil to about 17, and diminish its sanclincss projaoitionately ; 

 after a second flooding the soil so treated would consist of 76 parts of 

 sand and 24 of silt and clay, and the third year would see the sandy 

 soil converted into a loam composed of 70 per cent, of sand and .'30 

 per cent, of clay. 



King remarks, in connection with the similar deposits from the 

 Rio Grande, as follows : " When such sediments are laid down upon 

 coarse sandy soils, it will he readily appreciated that the gain to the 

 field is far greater than that due to the mere plant food which the 

 sediments contain ; for such sediments, being composed of very fine 

 grains, their influence in improving the texture of the soil is (juite as 

 great as that due to the fertilisers contained " * 



The Orange River clay, although rather heavier, appears in some 

 degree to resemble what has been called Vergennes clay, a type that 

 occurs on the terraces surrounding Lake Champlain, and consists^ of 

 deep-water sediments deposited in post-glacial times. The subsoil of 

 this clay, which more particularly resembles that from the Orange 

 River, is a heavy drab or light-brown clay, somewhat tenacious when 

 wet, but extremely stiff, compact and intractable when dry. The 

 Vergennes clay is said to be an excellent soil for hay; while corn, 

 oats and barley are also profitably grown. It 3'ielded, when examined 

 by the United States Department of Agriculture, the following 

 results : — 



Surface Soil. 



Subsoil. 



Fine gravel, 2-1 mm 

 Coarse sand, l-'5 mm 

 Medium sand, •5--25 nnn 

 Fine sand, '25-'l mm 

 Very fine sand, -l-'OS mm. 

 Silt, -OS-'OOS mm. 

 Chi}', less than -005 mm 



3 

 3 



18 

 69 





 1 

 2 



2 



2 

 22 

 71 



Nos. 2, 3 and -t illustrate the effect of the Orange River clay 

 being deposited on and mixed with the Kalahari sands which prevail 

 for many miles around. These sands are brick red in colour, and 

 constitute the coarser portions of the soils on the neighbouring fai'ms. 

 In the process of mechanical separation into grades the point of transi- 

 tion from the coarser red sands contributed to the soil by the Kalaliari 

 to the finer-grained drab-coloured silts derived from the river deposits 

 is readily distinguished. This sharp c<jntrast of colours enables one to 

 draw the inference tliat the silt deposits are often more coarsely grained 

 than that of whicli No. 1 is a sample. In each of the three soils 

 sampled the particles of greater fliameter than -1 inm. are of local 



* Iirifjatioa and /fj-"i/trigr, -iiid ed., 19U2, p. •J-U). 



