NATURE-STUDY LESSONS. 147 



12. (a) Where are the banks being worn away and 



where does deposition of materials take 

 place ? 

 (^) Why do these changes occur at these particular 

 places ? 



The wearing away of soil or rock by the influence of water and ice is 

 erosion. 



1 3. What causes determine whether erosion or deposi- 

 tion shall take place ? 



14. (a) Compare the points of erosion and deposition 



when the stream is at its ordinary height 



with similar points when the stream is at its 



flood height. 

 {i) Are these points always the same ? Why ? 

 (f) Compare the amount of erosion by swift and 



slow streams. 



15. (a) Are there any pebbles or stones in the chan- 



nel that do not belong to the rocks of the 

 district where they are found ? 



(6) Where have they come from and through what 

 agency ? 



{c) What is their shape ? 



{d) Account for this shape ? 



16. Examine the valley to determine whether the 

 stream has changed the location of its bed. 



17. (a) What determines the direction of the stream ? 

 {d) Account as far as possible for the bends in its 



course. 



18. (a) At a bend in the river, on which side is the 



water the deeper ? 

 (d) Account for the shallow water on one side and 

 the deep water on the other. 



