SOIL 



189 



particles of soil and rock with it into the valleys and 

 ravines. When the stream is swollen and the current 

 swift, large rocks are carried, and as they are rolled 

 along, they wear off the bottom and the sides of the 



Copyright by Henry G. Peabody. 



Fig. 72. Top of Jupiter Terrace, Yellowstone Park. Hot water 

 carrying mineral matter in solution comes to the surface in the 

 upper terraces. It then flows over the surface, and as it cools 

 the mineral matter is deposited. 



river bed, break off the edges of other rocks against 

 which they strike, and grind the finer rock particles 

 into 'the mealy powder which makes up the soil. As 

 the current slackens it drops its load, the larger, coarser 

 particles first, with the finer particles on top. 



This may be seen on any bottom land after the floods 

 have subsided. The frequent floods of these lands 

 account for their unusual fertility. Rocks are further 

 broken up by alternate freezing and thawing. The 

 water which has been absorbed into rock freezes, and 



