20 An Account of the Soil [pt. i 



forms it is so hard that it can only be powdered with 

 difficulty, it is also only very slightly soluble in water. 

 The sand on the sea-shore affords sufficient illustration 

 of its properties: in spite of the persistent hammering 

 of the waves, the washing of the sea and the rain, and 

 the exposure to all sorts of weather, it undergoes no 

 perceptible change in any period within the memory of 

 an individual ; the sand may be carried away but it does 

 not appreciably dissolve or break down under the in- 

 fluence of these agencies. The immediate ancestor of 

 sand is commonly a sandstone rock which is itself com- 

 posed of grains of sand united by some kind of cement- 

 ing material. When the rock was exposed to the action 

 of the weather the cement was washed away and then 

 the whole structure fell to pieces, grains of sand having 

 little or no power of holding together by themselves. 



This great resistance of sand to the action of water 

 and weather is its most striking property and gives rise 

 to consequences of great agricultural importance. It 

 gives up little or nothing to plants and hence is in no 

 sense a plant food: indeed plants quickly starve in it. 

 Its particles show very little tendency to break down 

 and remain for the most part rather large in size, vary- 

 ing, as we have seen, from 1 mm. (2^ in.) to 0-04 mm. 

 (bt5 ill-) ill diameter. Even the edges do not easily wear 

 away, and the particles remain irregular in outline. 

 Their large size and irregular shape prevent them from 

 packing very closely, and large pore-spaces are left in 

 between. Consequently air gets in very easily, water 

 rapidly flows through, and the sand speedily dries, at 

 any rate near the surface. 



Another very important group of mineral constituents 

 also contains silica, but in a state of combination with 



