40 CHEMISTRY, GEOLOGY 



although generally dry on the surface, are often 

 so wet below as to require drains to carry off the 

 excess of water. 



A drain should seldom be less than thirty 

 inches deep ; because the deeper the soil is made 

 dry, the deeper the roots of plants will descend 

 in search of food. If the drains are as deep as 

 thirty inches, the soil can be turned up with the 

 subsoil plough to the depth of nearly two feet, 

 without running the risk of injuring them. 



Draining is beneficial to the land for other 

 reasons. Drains admit air to the subsoil, and 

 they allow the rain to sink down and wash out 

 of it many substances which would be injurious 

 to the crops. It is not uncommon for crops, 

 which at first look very promising, to droop and 

 fail when their roots reach the injurious sub- 

 stances in the subsoil. 



Heavy or clay lands are often let stand as 

 permanent pasture, because the labor and expense 

 of ploughing and working them is so great, that 

 the crops of grain obtained from them do not re- 



Questions. How deep should drains be ? Why ? Do 

 you know any other reason for deep drains ? Of what 

 other advantage is draining ? Are crops ever injured by the 

 substances contained in the subsoil of unclrained lands ? 

 Why are clay lands often let stand in pasture ? 



