PREFACE. 



THIS volume was originally designed to serve as a text- 

 and reference book for the students attending the writer's 

 course on soils, given annually at the University of California, 

 who complained of their inability to find in any connected treat- 

 ise a large portion of the subject matter brought before them. 

 As all these students harl preliminary training in physics, chem- 

 istry and botany, no introductory chapters on these general 

 subjects were necessary or contemplated ; the more so as good 

 elementary treatises embracing the needful preparation are 

 now numerous. 



As time progressed, however, outside demands for a book 

 embodying the writer's soil studies in the humid and arid 

 regions, especially the latter, became so numerous and pressing 

 that the scope of the work has gradually been much enlarged 

 to conform to these demands ; and this, rather than com- 

 pleteness of detail, when such detail can be found well given 

 elsewhere, has been the guide in the necessary condensa- 

 tion of the whole. To give the entire subject matter full eluci- 

 dation, would require several more volumes. 



It may not be unnecessary to explain at the outset why and 

 how this treatise deviates in many respects from previous pub- 

 lications on the same general topic. From boyhood up it has 

 fallen to the writer's lot to be almost continuously in more or 

 less direct contact with the conditions and requirements of 

 newly settled regions, as well as with those hardly yet invaded 

 even by the pioneer farmer; where the question of cultural 

 adaptation was yet undetermined or wholly in the dark. Being 

 during his active life constantly called upon in his official capa- 

 city to give information and advice to pioneer farmers or in- 

 tending settlers in regard to the merits and adaptations of virgin 

 soils, the writer's attention was naturally and forcibly directed 

 toward soil investigation as a possible means of determining, 

 beforehand, the general prospects and special features of agri- 



