SOIL AND SUBSOIL. ! 79 



useless for cultivation. It is naturally covered with low, 

 stunted shrubs or chaparral ; only here and there, \vhere a cleft 

 has been caused by earthquakes or subsidence, a large pine tree 

 indicates that nourishment and moisture exists within the 

 refractory clay stratum, and suggests blasting as a means of 

 rendering the land fit for trees at least. 



No. 3 is a case similar to that of No. 2, only there is here a 

 dense unstratified mass of red clay, of good native fertility. It 

 is here that the expedient of blasting the tree holes with dy- 

 namite was first successfully employed, in central California. 

 For lack of this, extensive tracts of similar land in southern 

 California, planted to orchards, have completely failed of useful 

 results after three vears of culture. 



^ 



No. 4 shows a typical case of calcareous hardpan obstruct- 

 ing the penetration of roots, even though usually interrupted at 

 intervals, because of the formation occurring mostly in swales, 

 along which the sheets lie more or less continuously. Here 

 also, blasting will generally permit the successful growth of 

 trees and vines, whose roots frequently will, in time, wholly 

 disintegrate the hardpan and thus render the land fit for field 

 cultures. The depth at which such hardpan is formed usually 

 depends upon the depth to which the annual rainfall pene- 

 trates. (See below, page 183). 



Nos. 4, 5, and 6 all illustrate cases of intrinsically fertile, 

 very deep soils, shallowed by obstructions which in the case of 

 No. 4 are hardpan sheets, while in No. 5 the intervention of 

 bottom water limits root penetration, hence restricts the use of 

 the land to relatively shallow-rooted crops, and the use of only 

 a few feet of the profusely fertile soil. Such is the case where 

 bottom water has been allowed to rise too high, through the 

 use of leaky irrigation ditches. 



No. 6 illustrates a case not uncommon in sedimentary lands, 

 where bottom \vater is quite within reach of most plants, but is 

 prevented from being utilized by the intervention of layers of 

 coarse sand or gravel, through which the water will not rise: 

 and the roots, while they would be able to penetrate, are not 

 near enough to feel the presence of water underneath and there- 

 fore spread on the surface of the gravel, suffering from drought 

 within easy reach of abundance of water. The " going- 

 back " of large portions of orange orchards in the San Ber- 



