28 THE FERTILITY OF THE SOIL [CH. 



so, in determining the amount reaching the soil 

 (heavy rains being liable to run off the surface while 

 lighter rains soak in), and the temperature and 

 wind are great factors in determining how much 

 stays there. February is one of the driest months 

 so far as actual rainfall goes, but no one who lives in 

 the country need be reminded how persistently wet 

 the ground generally is then. August, on the other 

 hand, is one of the wettest months, but the soil is 

 usually dry. Equally important factors are the nature 

 of the surface soil, which determines how much of 

 the rain percolates ; the position of the soil in respect 

 of the surrounding land whether high or low lying 

 and the nature of the subsoil, which regulate the flow 

 of the underground water. 



A defective water supply may therefore be either 

 the fault of the soil or its misfortune. Too much 

 clay or peaty organic matter may render the soil 

 impervious to rain and so cause it to lie waterlogged, 

 while too much coarse sand or chalk may keep it so 

 open that water rapidly drains away or evaporates ; 

 in all these cases the soil is to blame. On the other 

 hand, the very best soils may remain stagnant marshes 

 if they occupy low-lying ground on which water 

 drains from the hills without finding an outlet; or 

 they may suffer badly from drought if they are 

 spread out thinly on beds of gravel or of rock. The 

 stagnant marsh may be drained and the soil soon 



