822 



Handbook of Nature-Study 



Where the stream drops its load. 



HOW A BROOK DROPS ITS LOAD 



Teacher's Story 



The brook is most discriminating in the way it takes up its burdens, and 

 also in the way it lays them down. It, with quite superhuman wisdom, 

 selects the lightest material first, leaving the heaviest to the last; and when 

 depositing the load, it promptly drops the heaviest part first. And thus 

 the flowing waters of the earth are eternally lifting, selecting, and sifting 

 the soils on its surface. 



The action of rain upon the surface of the ground is in itself an excellent 

 lesson in erosion. If there is on a hillside a bit of bare ground which has 

 been recently cultivated or graded, we can plainly see, after a heavy rain, 

 where the finer material has been sorted out and carried away, leaving the 

 larger gravel and stones. And if we examine the pools in the brook, we 

 shall find deltas as well as many examples of the way the soil is sifted as it is 

 dropped. The water of a rill flowing through pasture and meadow is 

 clear, even after a hard rain. This is owing, not so much to the fact that 

 the roots hold the banks of the brook firmly, as that the grass on the surface 

 of the ground acts as a mulch and protects the soil from the erosive impact 

 of the raindrops. On the other hand, and for a reverse reason, a rill 

 through plowed ground is muddy. On a hillside, therefore, contour plow- 

 ing is practiced that is, plowing crosswise the hillside instead of up and 

 down. When the furrow is carried crosswise, the water after showers can 

 not dash away, carrying off in it all the finer and more fertile portions of the 

 soil. There are many instances in our Southern States where this difference 

 in the direction of plowing has saved or destroyed the fertility of hillside 

 farms. 



The little experiment suggested at the beginning of the following lesson, 

 should show the pupils clearly the following points : It is through motion 

 that water takes up soil and holds it in suspension. The tendency of still 



