28 



Some experiments with the sand 



does so and makes a spring, or sometimes a whole line 

 of springs or wet ground. Rushes, which flourish in 

 such wet places, will often be found growing along this 

 line, and may, indeed, in summer time be all you can 

 see, the water having drained away. But after much 

 rain the line again becomes very wet. Fig. 14 shows 

 the foot of a chalk hill near Harpenden, where a spring 

 breaks out just under the bush at the right-hand side 



I^ig. 15. "The little pool below the tree" 



of the gate. In Fig. 15 the bush itself is seen, with the 

 little pool of water made by the spring. Here the water 

 flows gently, but elsewhere it sometimes happens, as in 

 Fig. 16, that the spring breaks out with great force. 



Now stop up the glass tubes so that the water cannot 

 get out. Soon the sand becomes flooded and is no better 

 than clay would be. A second model will show this very 

 well. Make a large saucer of clay and fill with sand : 



