98 THE PRINCIPLES OF 



decay gradually alter the nature of the sub-soil. There is at 

 Rothamstead a very interesting series, exhibited in glass 

 tubes of eighteen or twenty inches in diameter. Each of 

 these wide tubes contains a section of soil taken from the 

 surface to about three feet in depth, and there may be seen 

 the wonderful effect produced by drainage and by good 

 surface cultivation and liberal treatment in gradually altering 

 and modifying the sub-soil altering it from the condition of 



FIG. 2. Portion A B wet from accumulations of collected water below it which rises 

 up through it. E E E super-saturated portion of underlying soil. D B the water table. 

 A springs which overflow and help to wet the surface and injure vegetation. D D di-y 

 porous soil allowing of the free percolation of water. This diagram also illustrates 

 Elkington's system of drainage. 



a blue clay of a compact soapy texture, and converting it into 

 a red crumbly sub-soil which must be better in all respects for 

 the growth and development of crops. 



Taking up the subject where we left it, I pointed out in 

 the last chapter the difference between heavy lands and light 

 lands, either of which may be incommoded with surplus 

 water. Heavy soil is wet from the direct resistance it offers 

 to the passage of water through its mass. Light soils are 

 wet from the obstruction of a clay bed or other impervious 

 bed beneath the surface. If there is no such obstruction to 



