2IO ROCK GARDENS 



stones into the soil, it will be useful to have 

 an idea of the quantities required. 



One ton of dry sand contains twenty-four 

 and a half cubic feet in bulk. So by spread- 

 ing a ton one inch thick it will cover thirty- 

 two square yards, and a ton of broken stones 

 about twenty-five square yards. If either is 

 very wet, the bulk will naturally be reduced 

 as compared with the weight, and correspond- 

 ingly cover less area. 



Those who wish to make an artificial bog- 

 bed with concrete, as described in Chapter VII., 

 may find the following calculations of service. 

 For the foundation, one ton of broken stones, 

 laid six inches thick, will cover three square 

 yards. For the concrete, use it at a strength 

 of six to one. Take one bag of Portland 

 cement (weighing two hundred and eleven 

 pounds), and mix with eleven cwt. of gravel ; 

 this should give about thirteen cwt. of con- 

 crete, equal in bulk to about twelve cubic feet. 

 By spreading this three inches thick it should 

 cover about five and a half square yards. In 

 order to make the basin of the bog-bed water- 

 tight, a coating of pure cement will have to be 



