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formations which may exist in their terri- 
tory, has been recognized. In all these and 
many other even larger questions a knowl- 
edge of the variety and distribution of the 
soils of a territory is of prime importance. 
Principles of Classification—The study 
of any group of facts or phenomena in- 
volves an understanding of the properties 
in which they may differ, and the sys- 
tematic representation of these differences 
requires that the properties of importance 
be arranged and classified with reference 
to some controlling interest. Soil is no 
exception to this general rule, but the ap- 
plication of these principles in the field 
description of soils in a practical way and 
from the agricultural point of view pre- 
sents many and complicated problems. 
Definition of Soil—tn the discussion of 
the classification of soils, the soil should be 
viewed very broadly so as to include any 
portion of the earth’s surface capable of 
producing plants. It includes thin, stony 
material as well as that of great depth and 
friability. It meludes desert regions as 
well as humid regions. It includes the 
material as deep as any influence is ex- 
erted upon plants growing on the surface. 
Requisites of Scheme of Soil Classifica- 
tion.—The classification of soil to be of the 
largest value should effect the accurate 
separation of materials with reference to 
all important inherent agricultural dif- 
ferences. This statement indicates the 
breadth of the point of view to be taken. 
It is that of the farmer—agriculture in its 
broadest sense. The classification should 
not be confined to any particular section 
of plant production. It should apply to 
flowers and forests as well as wheat and 
eotton.. It should have a place for the 
roughest mountain region as well as for 
the most intensively tilled garden. To be 
less comprehensive is to invite arbitrary 
judgment and corresponding inaccuracy in 
SCIENCE 
[N.S. Vou. XXXV. No. 905 
the application of the scheme in the field. 
The distinctions with reference to plant 
growth and agricultural practise which 
should be made are differences in, first, 
chemical composition, including total con- 
tent of plant food, amount of lime, amount 
and condition of the organic matter and 
the solubility of all these, including the 
presence of alkali salts; second, physical 
properties including texture, structure, 
color, moisture capacity, aeration and 
temperature; third, the climate under 
which these properties exist. These dis- 
tinetions which will determine natural 
plant growth will also make sufficient pro- 
vision for agricultural practise necessary 
to produce domestic crops. 
The ideal result of the scheme of soil 
classificaton is to separate all soil material 
into types or individuals which are uni- 
form in their agricultural value and dis- 
tinct from every other type of soil. The 
soil type must be the unit and the pri- 
marily important separation in the scheme. 
Once the types are recognized they may be 
grouped according to any selected proper- 
ties, irrespective of those involved in ar- 
riving at their identity. 
Difficulties in the Field Separation of 
Soils—Having pointed out the properties 
with reference to which soils should be 
classified, the next problem is to apply these 
in a systematic way in the field. Herein 
arise two kinds of difficulties: First, to 
classify soils directly by their properties 
for plant growth is impracticable. Take 
chemical composition, for example. To 
classify soils upon the basis of chemical 
analysis of samples of every acre or even 
every ten acres is impracticable because of 
the large amount of labor and time in- 
volved. To directly determine the mois- 
ture capacity, temperature and other es- 
sential factors of plant growth presents 
similar practical difficulties. The direct 
