230 



ROCKS AND SOIL 



Demonstration 1. Solution of Limestone. 



Pass carbon dioxide into a jar of limewater. What happens? 

 This substance has the same composition as limestone. Now 



continue to pass the car- 

 bon dioxide into the jar, 

 and you will see the white 

 substance disappear. It 

 has been dissolved by the 

 extra carbon dioxide in 

 the water and has passed 

 into solution. 



Erosion. You have 

 all seen gullies cut in 

 the bank of the river 

 after a heavy shower, 

 and have noticed that 

 soil is carried down 

 by the water and dis- 

 tributed in a layer at 

 the foot of the gulley. A mountain stream shows the 

 same effect on a large scale. This wearing away and 

 carrying off of material is called erosion. Our mountains 



Streams play an important part in changing the 

 surface of the land. Explain how they do this. 



Wright Pierce 



Wind has caused these holes in the rock. How could it do this ? Read page 231. 



