203 



Rich though it may be chemically, the Orange River deposit contains 

 too much clay and is therefore too dense and heavy to enable it to be 

 advantageously used in its original condition; but when deposited on the 

 surface of a sandier soil, with which it may be manipulated, it would add 

 considerably to the agricultural value of the latter. If it could b directed 

 on to a very sandy soil, containing, say, 90 per cent, of sand, a single flood- 

 ing of the lands would assuming a half-inch annual deposit increase the 

 proportion of silt and clay in the soil to about 17, and diminish its sandi- 

 ness proportionately; after a second flooding the soil so treated would con- 

 sist 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. 



At a previous stage a remark of King in connection with the Rio 

 Grande deposits was quoted ; he continues the passage as follows* : 



" When such sediments are laid down upon coarse sandy soils, it will be 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 quite 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 yielded, when mechanically examined by the United States 

 Department of Agriculture, the following results : 



Surface soil. Subsoil. 



Fine gravel : 2 1 mm. ..... 2 



Coarse sand :1 '5mm. ... . 1 



Medium sand : '5 '25 mm. 2 2 



Fine sand: -25 -1mm. ..... 3 2 



Very fine sand : *1 '05mm. 3 2 



Silt: -05 -005mm 18 22 



Clay : less than -005 mm 69 71 



Nos. 2, 3 and 4 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 farms. In the process 

 of mechanical separation into grades, the point of transition from the 

 coarser red sands, contributed to the soil by the Kalahari, to the finer- 

 grained drab-coloured silts, derived from the river deposits, is readily dis- 

 tinguished. This sharp contrast of colours enables one to draw the infer- 

 ence that the silt deposits are often more coarsely grained than that of 

 which No. 1 is a sample. In each of the three soils sampled the particles 

 of greater diameter than 'I mm. are of local origin, whereas those below 

 that size are river-borne sands, silts and clays. No. 2, as the table 

 of results shows, becomes less sandy as one penetrates deeper, but Nos. 

 3 and 4 are sandier lower down than at the surface. 



As representing some of the choicest lands in those districts which 

 have been termed the Granary of the Colony, the two Koeberg soils num- 

 bered 33 and 34 amongst the Cape Division samples (vide page 

 39), were chosen for mechanical analysis. They have already 

 been described, and their chemical condition referred to. t Each of 

 these two soils was sampled, in twelve-inch vertical sections, to a depth 



* " Irrigation and Drainage," 2nd ed., 1902, p. 259. 

 fSee pp. 40 and 158. 



