ROGK POOLS AND PONDS 83 



out (it will come in for forming the base of the rock- 

 work) to a depth that will allow of the placing of the 

 concrete or other watertight material, and a depth of 

 water varying from two and a half feet to eighteen 

 inches in different parts. This varying depth is useful 

 for the accommodation of small aquatic plants, but for 

 Nymphaeas a uniform depth of about two to two and a 

 half feet is best. If the subsoil is light and porous, it must 

 be well beaten down and made as firm as possible, as 

 leakage is sometimes caused by its sinking. The sides 

 may either be quite upright or sloping, this depending 

 on the space available, though the latter is preferable. 

 About six inches from the intended water level a shelf 

 may be formed all round by making the hole there a 

 little wider. This is to allow for a margin of moisture- 

 loving plants. 



Forming the Pond. The material should then be 

 laid in the bottom and continued up the sides. Too 

 abrupt an angle at the junction of the bottom and sides 

 is not advisable, as leakage is more likely to occur if 

 this exists. If concrete is to be employed it is an 

 advantage to embed wire netting in it : a layer of con- 

 crete is put down, the netting laid on it and covered 

 by additional concrete. Some make concrete with 

 three parts of cinders and one of quicklime, mixed with 

 cement and water ; but the usual method is to employ 

 two or three parts of broken stone to one of Portland 

 cement, mixing these thoroughly with water. It is 

 better to give too much rather than too little cement. 



