148 NATUBE-STVDY LESSONS. 



(c) On which side of the bend is erosion taking 



place most rapidly ? 



19. How does a stream tend to straighten its course ? 



20. {a) In which part of the valley has the river its 



course ? 

 (l>) Account for the level stretches in the valley. 



21. (a) Examine any falls or rapids in the stream. 

 (l>) What determines whether there shall be falls 



or rapids ? 



22. (a) In what direction relative to the stream are 



the falls gradually moving ? 

 (6) Why? 



23. (a) If possible, examine the sides of the valley. 



(d) Describe them. 



24. What causes determine whether there is a gradual 

 slope or a bluff? 



25. What forces are at work tending to obliterate the 

 traces of the action of the river as you go back from 

 the river bed ? 



26. (a) Observe any small streams that flow into the 



river. 

 (3) In what direction do their courses lie with ref- 

 erence to that of the river ? 



27. (a) Examine the river where a tributary enters it. 

 (6) Are there any deltas or bar formations? 



Account for their presence or absence. 



28. What effect have tributaries upon the course of a 

 stream ? 



29. How does vegetation on the banks affect the char- 

 acter of a stream ? 



30. How do animals like beavers and muskrats affect 

 the river? 



