WEIGHT OF SOIL PER ACRE 45 



passage upward of the soil within the tube is so great that 

 the contents of the tube becomes less than that proper to the 

 depth reached. When the sample of the surface soil has 

 been taken in the manner described, the earth can be dug 

 away around the tube, and when the tube has been emptied 

 it can be again driven down, and a sample of the succeeding 

 depth obtained. At Rothamsted, the soil of the experimental 

 fields has been sampled in this way to a depth of nine feet. 

 The iron or steel frame employed at Rothamsted is square in sec- 

 tion, the sides of the square being six inches, and the depth 

 nine inches. Table IV shows the average weights of soil per 

 acre obtained at Rothamsted, Herts, and at the experimental 

 farm at Woburn, Beds, by the method just described. 



The weights here given represent soils in their natural con- 

 dition of consolidation. The pasture soil is of course quite 

 undisturbed by tillage, but in the case of the arable soils a part 

 of the upper nine inches has been so disturbed. The Rotham- 

 sted soil is a heavy loam, containing many partially rolled 

 flints ; it rests on a variable subsoil of loam or clay, beneath 

 which is the chalk. The Woburn soil is a light sand. The 

 stones mentioned in the Table were in every case separated 

 by a sieve having quarter-inch meshes. 



Looking first at the total weight of dry soil per acre, we 

 see that the soil is in every case lightest at the surface, and 

 increases gradually in weight as we descend into the subsoil. 

 This is in part due to the increasing pressure to which each 

 succeeding stratum of soil is subjected, and in part to the 

 result of particular actions tending to make the surface soil 

 loose and porous. The action of rain is to wash out of the 

 surface soil its finest particles, and to carry them into the 

 subsoil ; the surface soil is thus made up of coarser particles, 



