WATER. 65 



by percolation. Even on strong clay lands there are generally at 

 least 6 in. of surface-soil, which is more or less porous. Lakes 

 may be made water-holding by use of either cement or " puddle." 

 If the soil be sandy or gravelly, and no clay is available, and above 

 all, if a solid foundation can be found, then concrete may be used. 

 It should be deposited not less than 12 in. thick on the bottom and 

 1 8 in. at the sides, and should be composed by mixture of i part 

 of hydraulic lime with 4 parts of broken stone and sand, or i part 

 of Portland cement with 6 parts of broken stone and sand. This 

 is to be floated with a layer i in. in thickness of cement. Before 

 the concrete is laid, the natural bottom must be worked solid and 

 firm. The result is disappointing if the deposit be made on filled- 

 up ground, or on that which is liable to slip, or is otherwise unstable. 

 When puddle is used, many of the same conditions must be created ; 

 but there are two ways of using this material. It is made by obtaining 

 clay, then cutting it and cross-cutting it, pouring water on it, and 

 working- it in a mortar-mill, or by treading, till it is plastic. The 

 first way of applying the material is this : The ground being excavated 

 to the required depth, allowing for the puddle that is to be deposited, 

 the puddle should be laid not less than i ft. thick on the bottom 

 and 1 8 in. on "the sides. As it is laid, it must be well trodden and 

 rammed till the formation is complete and as homogeneous as possible. 

 The second method is more satisfactory, where it is available, and 

 that is when a bed or substratum of water-holding clay underlies the 

 surface at a moderate depth. The whole lake can then be made 

 water-holding by means of puddle-gutters (see Plan, Jig. A). Such 

 gutters should be based on the water-holding stratum reached by 

 cutting through the overlying soil. From that base must be con- 

 structed the puddle-gutter, or contained wall of puddle, to the height 

 of at least i ft. above the projected water-level. The gutter should 

 be in no part less than 18 in. thick, and should increase in thickness 



