210 SOILS 



uniting all into one main. The cases are rare 

 when it is best to let each line of tile have an in- 

 dependent outlet. 



The outlet should be kept clear of weeds and 

 soil, guarded from the tramping of animals and 

 protected from injury by frost. In the Northern 

 States it is not safe to run the ordinary soft tile 

 to the surface. The last ten feet, at least, 

 should be of more durable material, as a box drain 

 made of 2-inch plank; or, better yet, the last ten 

 feet may be of glazed sewer tile. Cast iron sewer 

 tiles are sometimes used. It is well to face the 

 bank at the outlet with brick or stone. There 

 should be a wire screen over the outlet to prevent 

 the entrance of small animals. Examine the 

 outlet at least twice a year to see that it is free. 



THE GRADE OF TILE DRAINS 



The amount of fall or grade that under-drains 

 should have depends upon the contour of the land, 

 the length of the drains and the character of the 

 soil. The first thing to do is to locate the outlet 

 above all possible danger from obstruction by back- 

 water. The height above the outlet of the highest 

 point of land that is to be drained must next be 

 determined. For example, there may be a dif- 

 ference of seven feet between the outlet and the 

 upper end of the main, and the distance is 1,200 

 feet. This means that the main may have a fall of 

 five inches per hundred feet, which is about right. 

 The main drain must follow the lowest land from 

 the outlet to the head of the drainage system, and 

 be given as much fall as possible, within a reason- 

 able limit, so that the lateral drains will have 

 sufficient fall. The fields that are most likely to 



