The Physical Character of Soils 23 



total amount of moisture in the soil. Professor King, in 

 his book on the soil, well illustrates this with the example 

 of a marble dipped in water. It will be surrounded by a 

 film of water. A marble one inch in diameter will hold a 

 film of water 3.1416 square inches in area. Reduce the 

 marble to spheres one-tenth of an inch in diameter and 

 their aggregate areas will be 31.416 square inches. Re- 

 duce the particles to one-hundredth of an inch and it will 

 take a million of them to fill a cubic inch, and they will 

 have a total area of 314.16 square inches. With soil par- 

 ticles only one-thousandth of an inch in diameter, it will 

 take one thousand millions to make a cubic inch; and 

 their aggregate surface must measure 3 141. 6 square inches 

 — all contained in the inch which, as a whole, had but 

 3. 1 41 6 square inches of surface. 



This illustrates in the plainest possible manner the way 

 in which moisture is held by soils of different physical 

 character. Naturally, in a cultivated soil there is a ten- 

 dency for the finer particles to settle downward between 

 the coarser particles, if they are of the same specific grav- 

 ity. Thus we find that in the wide areas that exist in 

 some countries Hke China, where the soil to a considerable 

 depth has been formed by finer particles blown by the 

 wind, there is a smaller percentage of extremely fine par- 

 ticles than where the soil is sedimentary clay that was 

 carried by water. The more sandy nature of this "loess" 

 soil, so called, makes it far more easy to cultivate than the 

 sedimentary clay which has a far larger percentage of fine 

 particles. Where the clay particles approach the fineness 

 of the five-thousandth of an inch, they are apt to be 

 agglomerated into larger masses and not to hold, each 



