SOIL AND SUBSOIL. 167 



some cases where by long cultivation and plowing to the same depth, a 

 compact soil-layer or plowsole has been formed, and the land is then 

 leveled for the introduction of irrigation. In these cases a section of 

 the soil mass will usually show a marked difference in color and texture. 

 But, as a rule, in taking soil samples, no noticeable difference can be 

 perceived between the first and the second, and oftentimes as far down 

 as the third and fourth foot. The extraordinary root-peneti'ation of 

 trees, shrubs and taprooted herbs, whose fibrous feeding-roots are found 

 deep in the subsoil and are sometimes wholly absent from the surface 

 soil, fully corroborate the conclusion reached by the eye. The roots 

 of grape vines have been found by the writer at the deptli of twenty- 

 two feet below the surface, in a gravelly clay loam varying but little the 

 entire distance. In a similarly uniform and pervious material, the 

 loess of Nebraska, Aughey 1 reports the roots of the native Shepherdia 

 to have been found at the depth of fifty feet. 



Resistance to Drought. These peculiarities of the soils of 

 the arid region explain without any resort to violent hypo- 

 theses, the fact tint many culture plants which in the regions of 

 summer rains are found to he dependent upon frequent and 

 abundant rainfall, will in California, and in the country west of 

 the Rocky Mountains generally, thrive and complete their 

 growth and fruiting during periods of four to six months of 

 practically absolute cessation of rainfall; when east of the 

 Mississippi a similar cessation for as many t^'ccks will ruin 

 the crops, if not kill the plants. In continental Kurope. in 

 1892, a six weeks' drought caused almost all the fruit crops to 

 drop from the trees, and many trees failed to revive the next 

 season; while at the very same time, the same deciduous fruits 

 gave a bountiful crop in California, during the prevalence of 

 the usual live or six months' drought. This was without irri- 

 gation, or any aid beyond careful and thorough surface til- 

 lage following the cessation of rains in April or May, so as to 

 leave the soil to the depth of live or six inches in a condition 

 ot looseness perfectly adapted to the prevention of evaporation 

 from the moist subsoil, and of the conduction of the excessive 

 heat of the summer sun. This surface mulch will contain 

 practically no feeding-roots, the paralysis or death of which 

 by heat and drought would influence sensibly the welfare of 

 the growing plant. 



1 See Merril 1 , Rocks and Rockweathering. 



