GEOLOGY IN RURAL WELFARE 
287 
soil distribution, largely in that of physiography. Different kinds 
of soils are produced from different kinds of rock, or from the 
same kind of rock when subject to different processes during the 
course of origin. For example, soil originating from a given 
kind of rock in a warm, wet climate will be very unlike those 
derived from the same kind of rock in a cool, arid region. A 
third kind of soil will result if the materials from the same kind of 
rock are transported and sorted by water before forming the 
final soil; a fourth kind if transported by glaciation; and a fifth, 
if deposited by the wind. The various kind of soil may differ 
from each other in number of mineral constituents or in the 
different proportions of such. The development of hills and 
valleys, and other topographic forms, by erosion gives rise to a 
different kind of soil in each topographic location. Kinds of soil 
arise also in numerous other ways each of which is a response 
either directly or indirectly to geologic or physiographic processes 
and conditions. 
Classification of soils, that they may be subjected to treatment 
conducive to the greatest production, depends chiefly on the accu¬ 
rate use of the principles of soil origin and distribution. The 
changes recently made by the United States Bureau of Soils in the 
revision of classification units that were used in mapping a number 
of years ago afford excellent illustrations of this fact and of its 
recognition by the Soil Survey. The new divisions formed are 
based almost wholly on genetic and topographic relations — the 
principles of geology and physiography being applied to a much 
greater extent and in greater detail than in the early work. 
Distribution of vegetation, in so far as it is controlled by 
topography, kind of rock and geologic structure, constitutes an 
important phase of agricultural geology. The distribution of soils, 
of rainfall, of temperature and of plant and animal life, the lo¬ 
cation of water-courses, of valleys and uplands, of railways, high¬ 
ways and of markets, as well as the adaptability of various areas 
to their respective agricultural uses, are, to a remarkable extent, 
arranged in accordance with the topography and with the kinds 
and relations of the underlying rocks. 
The principles of improvement in domestic plants and animals 
are found in a diligent study of the geological history of their 
