THE ECONOMIC ASPECTS OF SOIL EROSION 
By Dr N, S. Shaler, 
Professor of Geology in Harvard University and Dean of the Lawrence 
Scientific School 
The old view that the earth was firm set and that on it we could 
build “ for aye ” has gone the way of many ancient opinions. 
In every region which geologists have investigated they have 
had occasion to note many and profound alterations in the form 
of the surface which have taken place since man has occupied 
the earth. The}" have come to recognize the fact that man him- 
self is, through his arts, particularly those of agriculture, one of 
the great agents of change, and that through these interferences 
with the course of nature the operation of many foz’ces has been 
greatly increased in energy. This understanding has extended 
beyond the class of special students of earth phenomena. M"e 
find, indeed, the ablest essay as to the influence of man on ter- 
restrial conditions written by one who approached the subject 
from the standpoint of the historian. So far as I am aware, no 
geologist has yet undertaken to consider this matter with refer- 
ence at once to its scientific aspect and its economic importance. 
I therefore propose to take up the processes of land erosion from 
the point of view of the geologist, and to tz’ace the influence of 
their actions upon the formation and izreservation of the soil. 
In the treatment of this subject we shall he led into that im- 
portant but as yet unrecognized branch of national economy 
which relates to the preservation of the tillage values of various 
countries. 
In dealing with any group of geological features, it is well to 
consider at the outset the origin and mode of application of the 
energy that has served to give them shape. 'We may therefore 
begin our task with a brief account of the forces which operate 
in the jn-ocess of erosion. So far as regards their origin, these 
forces are essentially simple. They all substantially depend 
upon solar radiation. Only secondarily and in a very unim- 
portant way are the}'' due to subterranean action or to the attrac- 
tions of the sun and moon, which give rise to the tides. The 
average amount of heat received by a square foot of the earth’s 
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