THE DRAINAGE OF FARM SOILS 205 



drain off the surface water of nearly level fields as 

 effectively as lands twenty to twenty-five paces 

 wide, "because not enough water is carried into 

 any one of the dead-furrows to produce a current 

 sufficient to overcome the obstruction offered by 

 clods and friction." Surface drainage by dead- 

 furrows is most practicable on very fine clay soils, 

 through which water passes so slowly that it would 

 be almost useless to lay tile drains beneath them. 

 Sometimes the dead-furrows may be joined by 

 cross furrows, so as to convey the water away along 

 a natural depression. 



THE ACTION OF UNDER-DRAINS 



In most cases under-drains are more efficient 

 and more practicable than surface drains. Under- 

 drains may be of stone, boards, brush, or other 

 materials, but tile drains made of baked clay are 

 now used almost universally. Drain tiles have 

 come into common use within fifty years. There 

 are now many thousands of tile factories at work in 

 the United States. Any clay that will make good 

 bricks is suitable for making tiles. Few parts of 

 the country where tiles are most needed, especially 

 east of the Mississippi, are without facilities for 

 making drain tiles. 



The philosophy of under-drainage is simple. 

 An open passage is made through the soil below 

 the water-table; that is, below the point at which 

 water fills all the spaces between the soil particles. 

 It is like boring a hole into a water tank two feet 

 below the point where the water stands in the tank, 

 and inserting therein a pipe. The water is lowered 

 to the level of the bottom of the pipe. Lines of 

 3-inch tiles are run through the subterranean 



