CHAPTER IV 

 RECORDS LEFT BY RIVERS 



WHEN we come to examine more closely the work 

 which rivers do in removing mineral substances 

 from the land by washing particles of them 

 from the surface, we find that the records they leave in 

 geological history must be plainly marked. Every stream, 

 large or small, is always busy carrying mud, sand, or 

 gravel. Rivers are the " navvies " of geology. When they 

 are swollen by rain they sweep large stones away with 

 them. If we look at the bed of a mountain torrent we shall 

 often see huge blocks of stone that have fallen from the 

 cliffs on either side blocking the pathway of the stream. 

 To all appearance the stream is quite powerless to remove 

 these blocks, and has to circumnavigate them. But visit 

 such a torrent when the snows are melting, or heavy rain 

 has fallen, and you will hear the stones knocking against 

 each other or on the rocky bottom as they are driven 

 downwards by the flood. It is not easy to estimate the 

 driving power of water. M. Gustave le Bon has furnished 

 an illustration of its power which is very curious. In the 

 south of France a stream is led downwards from the 

 mountains to drive the turbine of some machinery at 



