CHAPTER XI. 

 A SHORT LESSON ON SOIL. 



WHEN the earth's surface cooled in former ages, it probably 

 formed solid rock. This was acted upon by wind, water, heat, 

 and frost and gradually became broken up into small particles 

 which formed inorganic soil. This process is still going on 

 and the results can be seen, for example on hills around 

 Cradock, where the sandstone in weathering, splits apart by 

 concentric coats, into sphere-like pieces. The soil particles 

 are washed or blown down from the mountain tops to the 

 valley where vegetation may appear which then plays its part 

 in the breaking-up of rocks. Fig. 1 16 shows the effect of wea- 

 thering. Soil has been formed on the slopes and at the foot 

 of the mountain range which shows the weathering sandstone 

 above. Inorganic soil is formed of such elements as calcium, 

 magnesium, silicon, sodium, sulphur, phosphorus, potassium 

 and iron combined with oxygen. 



In travelling through the country different characters of 

 soils frequently attract attention, chiefly by their difference in 

 colour. There are the light yellow and brick red sandy soils, 

 black and brick coloured clayey loam, light and dark chocolate 

 soil and the rich red volcanic soil, the basaltic lavas of the 

 Drakensberg. 



In gardens, wooded kloofs, under old Olive trees and 

 Ja4chals-Besjes bushes (Sideroxylon, Melkhout), rich dark soil 

 is found, called humus. This consists largely of organic 

 remains of plants and animals and contains oxygen, hydrogen, 

 nitrogen, and carbon. Humus which is poorly drained and 

 becomes acid is known as Peat. 



A fertile soil depends partly upon mechanical structure, and 

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