SUMMARY 361 



doing little if any erosive work. Rivers sometimes de- 

 velop flood plains through which they wander in S-shaped 

 meanders. Sometimes a river cuts back its divide so far 

 that it reaches another river, thus diverting another 

 stream through its channel. 



If the region of a river becomes elevated, the river may 

 be revived, and if it is an old river with meanders, in- 

 trenched meanders may be formed. Sometimes the eleva- 

 tion of the land causes a river to be laked or reversed ; if 

 it maintains its previous course in spite of the elevation, 

 it is called antecedent. 



If a river region becomes depressed, the river may be 

 drowned and its branches may enter the sea separately as 

 dismembered rivers. Many rivers build deltas where they 

 empty into still bodies of water and when the slope is 

 steep, they may form fans. 



Rivers have always played a great part in history, from 

 the time Egypt was first called the " Gift of the Nile " to 

 the influence of the Mississippi and St. Lawrence on the 

 settlement and development of the United States. 



QUESTIONS 



What conditions influence the amount of rainfall of a place? 



What determines what will become of the rainfall when it falls 

 upon the ground ? 



What does the water do which sinks into the ground? 



Where are geysers found ? What are they ? 



Trace the probable journey of the water that fell near your home 

 during the last heavy rain until it reaches its journey's end. 



What determines whether a lake is fresh or salt? What are the 

 great benefits derived from lakes ? 



Describe some effects of running water that you have seen . 



Why does not all the water that fell in your town during a heavy 

 rain flow by your home ? Where is the ' divide ' ? 



What are some of the causes which have formed falls and rapids ? 



