x.] SANDY SOILS 319 



tegration of shells, so that it is rich in calcium 

 carbonate ; but, as a rule, sandy soils are characterised 

 by poverty in this material. Most soils of this sandy 

 type seem to possess considerable amounts of oxide 

 of iron ; the actual proportion present may not be so 

 large as in ordinary soils, but, being spread over the 

 comparatively small surface offered by the large grains, 

 it is more in evidence. The phosphoric acid, which 

 is rarely present in any quantity, generally about 01 

 per cent, is chiefly combined with the oxides of iron. 

 Because of the general lack of finer particles in the 

 main clay derived from the weathering of felspar 

 soils of this type are notably deficient in potash. 



Despite their warmth and free aeration, sandy 

 soils often accumulate considerable amounts of humus, 

 an effect due to the absence of calcium carbonate. 

 Where depressions occur in the general level of the 

 ground, a layer of impervious ferric hydrate or "pan" 

 forms below the surface and holds up the drainage 

 water, which waterlogged condition is at once followed 

 by an accumulation of peat. 



On these sandy areas cultivation is a very artificial 

 affair, and the soil has practically to be created. The 

 first necessity is a supply of lime and mineral salts, 

 to remedy the lack of nutriment ; then as much humus 

 as possible must be obtained, by turning in or fold- 

 ing green crops, or even from their roots and stubble 

 only. The humus binds the soil together, creates a 

 reserve of manurial material, and much increases the 

 retentive power of the soil both for water and mineral 

 salts. 



Being so dry, the specific heat of sandy soils is 

 exceptionally low ; in consequence these soils are 

 early, and as they also recover quickly from rain, so 

 that cultivation is not forced to wait much on the 



