32 THE PRINCIPLES OF 



of pure sand and pure clay would therefore be hopelessly 

 unfertile, but a mixture of native sand and native clay would 

 not be barren, because the sand, as well as the clay, is inter- 

 mixed with materials which entitle it to the name of a 

 calcareous sand. There is likewise micaceous sand a sand in 

 which we find small sparkling plates of mica. While, there- 

 fore, quartzoze sand would be entirely sterile for purposes 

 of plant nutrition, yet when it is calcareous or micaceous in 

 character, we have the importation of fresh materials in the 

 same way as we have the importation of materials into clay. 

 Sand, therefore, in its crude or native state may add to the 

 fertility of the soil. 



The mechanical effect of sand is the reverse in many 

 respects to that of clay. Silicious sand has very little retain- 

 ing power for water. Its absorptive powers with regard to 

 water are nil. Expose it to a damp atmosphere, and it will 

 not perceptibly increase in weight. But expose dried clay 

 to the evening air, and we shall find that it will increase very 

 perceptibly in weight. The powers or capacity of sand for 

 holding water as a sponge holds water are very small com- 

 pared with clay. Its power of transmitting water or parting 

 with water is great. 



We have here a substance eminently adapted for diluting 

 or neutralizing the characters of a clay soil. Bring the two 

 together, and we produce a substance approaching very closely 

 to the proper conditions of a fertile soil. A loam is simply 

 sand and clay mixed together. I purposely avoid suggesting 

 percentages, and would warn my readers against any elaborate 

 classification of soils the classification proposed by Schubler 

 about forty years ago, and which appeared in the Journal 

 of the Royal Agricultural Society, has never been adopted. 

 The terms are good if not too rigidly employed; but as for 

 distinctly making a classification based on percentages of 

 ingredients, it is not practicable. 



