CHEMICAL NATUEE OF SOILS 349 



the laws governing its fertility and its rejuvenation when that 

 fertility becomes exhausted. Such a method of treatment is, 

 however, far beyond the limits of the present work, and we must 

 content ourselves with merely touching upon a few of the most 

 salient points, leaving the at present little understood subject 

 of fertility for other and abler writers. It may be well to re- 

 mark, however, that a soil left to itself and nature's processes 

 rarely becomes barren or exhausted except it may be under 

 changed geological conditions. A growing organism takes 

 temporarily from the soil that which is essential, but restores 

 it again with accrued interest in the form of carbonaceous and 

 nitrogenous matter derived from the atmosphere, when it dies. 

 Thus, under normal conditions, the soil grows yearly richer 

 and richer and capable of supporting larger and more luxuriant 

 crops. It is only when the husbandman comes in, and by his 

 improvident harvesting robs the soil not merely of its interest 

 due, but of a part of the principal as well, that bankruptcy 

 results. 



For a long period the fertility of a soil was felt to be dependent 

 very largely upon its chemical composition, and older treatises 

 and reports of geological surveys are filled with tables of analy- 

 ses which the acquired knowledge of years now shows us to be 

 almost worthless, either for the purposes for which they were 

 first intended, or as indicative of the mineral nature of the soil 

 itself.^ A soil which, under certain conditions of climate or 

 moisture, is utterly barren may, under changed conditions, be 

 fruitful in the extreme, as has been repeatedly demonstrated in 

 the case of the so-called American deserts, dreary stretches of 

 aridity given over to sage brush and a few degraded forms of 

 animal life, but which need only moisture to cause them to 

 laugh with harvests. 



Naturally, a soil containing in itself nothing in the way of 

 available plant food can be made to produce crops only when 



^ The common practice of making soil analyses, whereby the results are 

 tabulated as soluble and insoluble (meaning by soluble the portion extracted 

 by boiling hydrochloric acid) and putting down the latter as silica (or 

 sand) and insoluble silicates, cannot be too strongly condemned. It means 

 nothing. A growing plant is capable of extracting only a small, and as 

 yet unknown, portion of that taken out by the acid, and as to what silica 

 and insoluble silicates may be, we are left in ignorance. Such analyses are 

 satisfactory to neither the student of soils nor of geology. When quoted in 

 this work it is merely because nothing better is available. 



