26 CALIFORNIA FRUITS: HOW TO GROW THEM 



epochs, as well as slack-water deposits of the present epoch, all of 

 which are substantially independent of climate. While "sand" in 

 the humid regions means virtually quartz grains only, in the arid 

 country it means very largely grains and powder of the other soil- 

 forming minerals as well. While, therefore, in the humid region 

 sandy land as a rule means poor land, in the arid, on the contrary, 

 sandy lands are at least as desirable as heavier ones, both on the 

 score of high productiveness, durability, and ease of cultivation, 

 together with ready resistance to drouth. 



Depth. Another point of great importance is that the difference 

 between soil and suboil, which is so striking and important in 

 regions of abundant rainfall, is largely obliterated in arid climates. 

 Very commonly hardly a perceptible change of tint or texture is 

 found for depths of several feet; and what is more important, 

 material from such depths, when thrown on the surface, oftentimes 

 subserves the agricultural uses of a soil nearly or quite as well as 

 the original surface soil. The unconcern with which irrigators pro- 

 ceed to level or otherwise grade their land, even though this may 

 involve covering up large areas of surface soil with subsoil from 

 several feet depth ; the rapidity with which the red loam of the 

 placer mines of the Sierra Nevada foothills is re-covered with the 

 natural forest growth of the region, etc., are examples familiar to 

 the residents but surprising to newcomers, who are accusomed to 

 dread the upturning of the subsoil as likely to deprive them of re- 

 munerative crops for several years, until the "raw" subsoil has had 

 time to be "vitalized" by the fallowing effect of the atmosphere, 

 and to acquire the needful amounts of organic matter or vegetable 

 mold. Thus the surface soil, which in the humid regions supplies 

 the bulk of the nourishment, becomes here of minor importance, 

 serving chiefly as a mulch to prevent waste of moisture ; while the 

 active process of nutrition occurs in the deeper portion of the soil 

 stratum, whose composition, as well as condition of disintegration 

 and aeration, is substantially the same as above. The second foot is 

 rarely found to differ materially from the first, even as to content of 

 organic matter ; for the latter, being almost exclusively derived from 

 the decay of roots, the leaves and herbage on the surface being 

 mostly oxidized away under the intense heat and abundant aeration 

 of summer, it not uncommonly happens in very porous soils that the 

 first six inches of surface soil are poorer in organic matter than the 

 second foot. 



Practical Results of Lightness and Depth. The "lightness" and 

 perviousness of the prevailing soils of the arid region permit of the 

 penetration of roots to depths which in the humid region are inac- 

 cessible to them on account of the dense subsoils, which prevent the 

 needful access of air. This deep penetration enables even annual 

 plants to avail themselves directly of the stores of moisture in the 

 substracta, at depths which in the humid region are scarcely reached 

 save by the tap-roots of some prennials and trees ; while the latter 

 themselves reach depth never approached by them in the region of 

 summer rains. Professor Hilgard found the ends of the roots of 



