28 Light and Deep Soils. 
quirements in the event of exhaustion from too long cropping. 
This information must be sought in a number of publications, 
and no condensed outline of the work in its present state is avail- 
able. Professor Hilgard has now (1899) in preparation a general 
treatise entitled “Soils: Their Formation, Properties, Composition 
and Relations to Climate and Piant Growth,” which will natu- 
rally include the results of his long study of California soils and 
climates. It is the purpose of the writer to undertake a compila- 
tion, from these sources, of information which especially relates 
to the fruit soils of California, now known and used as such. 
The plan will be to collate the descriptions of the soils and their 
composition with the practical deductions therefrom, rather 
than the detailed analyses, for which the reader must be referred 
to the original source. 
DISTINCTIVE CHARACTERS OF CALIFORNIA SOILS. 
One of the most interesting and important recent achieve- 
ments in soil investigation consists in demonstrating distinctive 
differences between soils formed under arid and under humid 
climatic conditions.* In the development of this subject certain 
distinctive characters of California soils clearly appear and they 
are of direct relation to the thrift, productiveness, treatment and 
longevity of fruit trees. These characters are: (a) lightness and 
consequent permeability and ease of cultivation; (b) depth, ad- 
mitting exceptional root extension and penetration; and (c) rich- 
ness, containing some kinds of plant food in considerably 
greater amounts than are found in the soils of humid regions. 
These characteristics as demonstrated by Professor Hilgard may 
be outlined in this way with special reference to their relations 
to fruit growing. 
Lightness.—California soils predominantly exhibit the sandy, 
silty or pulverulent nature of all soils formed under arid condi- 
tions, save in case of pre-existing clay formations of former geo- 
logical epochs, as well as back-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 pow- 
der 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 ories, both on the score of high productiveness, dura- 
bility and ease of cultivation, together with ready resistance to 
drouth. 
Depth—Another point of great importance is that the dif- 
ference between soil and subsoil, which is so striking and im- 
* Rep. Cal. Exper. Stations, 1893-4, Pp. roo, 
