CHAPTER V 

 THE SOIL 



IF we dig a hole in the ground we usually notice certain 

 changes in the appearance of the earth which we remove 

 as we go deeper and deeper. That near the surface is 

 often dark in colour and loose or friable ; below this we 

 come in succession upon material of a lighter colour, 

 then probably a rather compact layer with stones, and 

 finally hard rock. If we look at a place where a deep 

 trench has been dug, as, for example, in a road-cutting, 

 quarry, or excavation for the foundation of a house, 

 or where a heavy rush of water has cut away the soil, 

 we see that there is a gradual change in appearance 

 from the upper to the lower layers. The stones of the 

 lower layers are probably of a similar material to the 

 rock at the bottom ; similarly the small stones and even 

 the finest particles which can be picked out are often 

 recognisable as fragments of the rock which lies beneath. 

 In other words, we see that soil largely consists of rock 

 broken up into small particles. 



This breaking-up results from the action of various 

 agencies, but is very largely due to water, containing 



carbon dioxide in solution, which dissolves carbonate of 

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