BROOK'S TOOLS AND ITS WORK 233 



carried them down they dug into the soil over 

 which they passed, gradually making the channel 

 deeper. Each stone did a little, and altogether it 

 made a great deal of digging. The stones, too, 

 began to be more rounded. They were scoured 

 clean by the sand which the water carried along. 

 After a heavy rain the stream would be so much 

 bigger that it could carry more stones and dig the 

 channel still deeper. The stones and the sand 

 were its tools then- and in all the thousands of 

 years since. Just as a carpenter uses his sand- 

 paper, and the cook her sapolio, so the brook 

 uses the sand and pebbles and boulders. The 

 great difference between the carpenter, the cook 

 and the stream is that the latter never lays down 

 its tools. From sunrise to sunrise, year in, year 

 out, century after century it works. No wonder 

 its tools are kept bright, though well worn ! 



"Now when the spring floods come we see the 

 surface of the soil loosened and perhaps carried 

 by the small stream off into the larger one. Thus 

 the permanent stream is provided with fresh tools 

 as the old ones wear out, and an increased power 

 to carry them. The stream even institutes land- 

 slides on its own account. Haven't you noticed 

 how the constant action of the flowing water has 

 'eaten in' under the sides of our gorges? When 

 the weight borne up by this overhanging bank 

 becomes greater than it can bear unsupported, it 

 falls, bearing with it into the stream's bed all its 

 load of trees, stones, leaf-mold and wild flowers. 

 I have seen streams which I thought rather over- 



