184 



87. — A pot-liole cut in the rock 

 of a stream's bed. 



thicker than others, showing a longer period of flood or perhaps 

 several floods in which there was little variation. This straiificatiou, 



as it is called, is one of the peculiarities 

 of water deposits and it is due to the as- 

 sorting power of currents which vary in 

 force. If we were to cut into the delta 

 we should And the same thing to be true 

 — a regular succession of layers though 

 sometimes confused by changes in direc- 

 tion of flow. 



To-day we shall notice something which 

 escaped our attention when it was held by 

 the rushing torrent — the valley bottom is 

 much wider than the bed of the stream ; if we keep our eyes open we 

 shall see the explanation of this in the abandoned channels, where, 

 owing to some temporary obstructions, the stream has been turned 

 from side to side of the valley, now cutting on one bank and now on 

 the other. In this turning from side to side the cutting area of the 

 stream is increased and it goes on widening its valley as well as cut- 

 ting it downward. 



And now we have learned some of the most important ways in 

 which the busy brook is toiling ; but there are other points which 

 we might have seen, and in some brooks there are special features 

 to be noted. However, we have learned that the brook is no idler, 

 that its main purpose is to conduct to the ocean the rain that falls 

 upon the earth's surface, and that in doing this it is wearing down 

 the hills, carrying them away only to build up in other deposits. 

 The cheerful song of the brook takes on a new meaning as we lie 

 in the shade and watch it hurry by. It is not the song of idleness 

 nor pleasure, but the song with which a cheerful and tireless worker 



seeks to make its task lio^hter. 



536 



