638 SOILS: FnOPBBTIBS AND MANAGEMENT 



tion of an underdrain. Many methods and materials 

 have been employed. One used in England in clay soil 

 is termed mole drainage. A plow having a long, thin 

 shank, with a molelike or cigar-shaped point at the 

 bottom, is slowly drawn through the soil by teams or a 

 capstan. The passage formed persists for several years 

 in the finer and more coherent classes of soil, and may 

 do good service. Soil free from stones and having a con- 

 siderable degree of plasticity is necessary for this method 

 to have much value. 



In ancient times, and in pioneer days in America, 

 bunches of faggots, brush, poles, rails, straw, and wooden 

 boxes of triangular or square shape, have been extensively 

 employed for underdrainage and have been very useful. 

 They may still have some use, but they have generally 

 been superseded by more permanent, if not more efficient, 

 materials. 



538. Stone drains. — "Wherever stones are abundant 

 they have been placed in trenches in some manner and 

 often have served for many years to facilitate the removal 

 of excess water from the soil. Where there are flat stones 

 they may be arranged to form a continuous throat. 

 Several systems of arrangement have been used. All 

 throated drains are more likely to be closed by sediment 

 than a drain with no single, distinct throat. Perhaps 

 the safest arrangement is to place flat stones on edge in 

 the trench, with their faces parallel to one another and 

 to the walls of the ditch, depending on the irregularities 

 between their faces for the flow of the water. Flat stones 

 are placed over the top of the vertical stones. Where 

 round stones are available the safest method is to place 

 them in the trench without any arrangement except to 

 put the smaU stones on the surface. The water will find 



