370 
THE ECONOMIC ASPECTS OF SOIL EROSION 
In considering the destruction which the elemental conditions 
bring upon a country which is subjected to the tax of civiliza- 
tion, the most imjjortant fields to be noted are those of the high- 
land districts, for the reason that there the slopes are, on the 
average, steepest, the rainfall is greatest, and the action of frost 
is most considerable. There the process of erosion is the mo.st 
rapid and the results are the most irremediable. There are, 
however, no lands in tliis country or in any other where the 
waste due to tillage is not notewortliy. Even in tlie prairies, 
where the average declivity of tlie surface is not more than one 
or two degrees, tlie effect of that baring of the earth which is the 
necessary first ste)) of tillage is to send a share of the earthy 
matter from the fields to the streams and thence to the seas. 
The close observer who will walk for a day during a time of pro- 
tracted rain along the banks of a main stream is likely to fiiul 
that some of the tributaries carry water which is nearly clear 
while others discharge a verN' muddy flow. Examining the 
cause of the difference he will note that the relatively clear 
brooks come from fields that are not tilled, being either in forest 
or grains, while tho.se which are very muddy have a large ]>ro- 
portion of their area under plow culture. While the destruction 
of a plowed field in a given time is greater in jwoportion to the 
steepness of its slope, there are practically no fields, however 
slight their declivity, which are not exposed in the same consid- 
erable measure to this kind of wasting. In a degree it is the 
inevitable accompaniment of tillage, which rests on the jdan of 
expelling the natural growth of a soil that place may be made 
for artificially imposed vegetation. However carefully the work 
may be done and whatever the nature of the crop, the earth is 
for the time bared to the a.s.saults of rain and wind. 
The question may well be asked whether, if this loss b}^ erosion 
is a neces.sary element of tillage, it is not certain that in time all 
the soils will go on their way to the sea, and the earth thus be 
made unfit for the uses of man. The answer to this is that the 
natural regimen of the soil provides a way by which a certain 
amount of waste in its mass may be in almost all cases made 
good through the decay of the underlying rocks. This is accom- 
plished by the action of that part of the rain-water which does 
not flow over the surface but finds its wa\’^ into the .soil and is 
slowly yielded to the streams in the form of distinct springs, or 
more commonl}" in the broad sheet of water which flows down 
along the bed-rock or the hard-pan until it enters the drain- 
