48 THE MECHANICAL ANALYSIS OF SOILS [chap. 



In this country it is customary to take a sample down 

 to a depth of 9 inches as representing the soil proper ; 

 it is, however, doubtful if this is not too deep, being 

 below the depth to which cultivation is generally carried ; 

 probably a 6-inch sample would more truly represent the 

 cultivated soil. In many cases it will be found that the 

 true soil does not extend to a depth of anything like 9 

 inches, but that there is a sharp change into subsoil or 

 even rock before this point : e.g., on the chalk downs the 

 soil is often not more than 4 inches deep, below which 

 white broken chalk rock begins. In such cases the 

 sample must only be taken to the depth at which the 

 visible change begins. 



To obtain the sample two methods are generally 

 adopted. At Rothamsted a steel box, without top or 

 bottom, 9 inches deep, and 6 inches square in section, is 

 used ; the sides are wedge-shaped, about f inch thick 

 at the top and tapering off to cutting edges below. 

 The surface, if uneven arable land, is first raked over 

 and gently beaten level, then the box is placed in 

 position and driven down with a heavy wooden rammer 

 till the top of the box is flush with the surrounding 

 soil. The soil enclosed by the box is then carefully dug 

 and scraped out into a bag for conveyance to the labora- 

 tory; two or three samples to the same depth being 

 taken from the same field and afterwards mixed. 

 Should samples of the subsoil be required, the box 

 is left in position after its contents have been scraped 

 out, and the surrounding soil is dug away to the 9-inch 

 level, the box is then rammed down for the second 

 9 inches, and its contents removed : the process being 

 repeated till the required depth has been reached. 



A modification of the Rothamsted method consists in 

 marking out on the surface a square 9 inches on the 

 side, and digging away the surrounding soil until a 



