230 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1949 
materials, soil science is not easily classified as a science in the tradi- 
tional patterns. Often it is included with the physical sciences, like 
chemistry and physics. Yet it is also grouped as correctly with the 
biological sciences, along with plant physiology and bacteriology. 
Then again, soil science is appropriately grouped with geology and 
geography as an earth science. Actually soil science uses the prin- 
ciples and methods of all three of these groups, and a soil scientist 
who uses the principles of only one or two of the groups, to the exclu- 
sion of the others, can only have small principles that have little 
prediction value and soon bog down in contradiction. In addition 
to those already mentioned, there are important principles and 
methods peculiar to soil science itself that do not belong to any other 
science. In application, the principles of soil science must be inti- 
mately related to those of the social sciences. 
It needs to be emphasized that the experimental method and the 
method of scientific correlation are essential in both fundamental 
soil science and in the application of its principles to practical prob- 
lems in farming, gardening, and forestry. 
Soils must be studied in relation to one another and to the whole 
environment, both natural and cultural, to understand their forma- 
tion and the influence of the individual factors of climate, vegetation, 
parent rock, relief, and time. How any one of these factors operates 
depends upon the others. The significance of any one soil charac- 
teristic depends upon the others. Any soil is a combination of 
characteristics, produced by a combination of factors, each of which 
influences the functioning of the others. 
Experiments are needed, both natural and artificial, to learn how 
individual soils behave and how they respond to treatment. These 
must be specifically related to individual kinds of soil, however, if the 
results are to be used in developing principles or as the bases for 
practical predictions. Thus the experimental methods and the 
methods of scientific correlation are intimately interwoven in produc- 
tive research in soil science. 
SOIL AND LANDSCAPE 
Let us look briefly at the implications of this concept of soils. They 
are natural bodies, each with its own unique morphology; they are 
dynamic bodies, developing with the natural landscape itself; they ac- 
curately reflect, at any moment, the combined or synthetic influence of 
the living matter and climate, acting upon the parent rock through 
processes conditioned by relief, over a period of time; they are dis- 
tributed over the earth according to orderly discoverable and definable 
geographic principles. 
The geological process of mountain building, rock formation, and 
landscape evolution from which the parent materials of soils originate, 
