THE BOG GARDEN 107 



the overflow and prevent the risk of flooding 

 the rock garden. The bottom of this control- 

 ling hole should be made a foot or more above 

 the bed of the stream, in such a way that the 

 wall below this hole will act as a dam. The 

 advantage of constructing it in this way is that 

 the sand and mud washed down by heavy rains 

 will be checked at the wall and not carried 

 down into the garden. 



This accumulation of sand and mud must be 

 cleared out periodically, otherwise the dam will 

 cease to be of any benefit. 



