100 DRY-FARMING 



particles, to form one lineal inch. The clay particles 

 are often smaller and of such a nature that they can- 

 not be accurately measured. The total number of 

 soil particles in even a small quantity of cultivated 

 soil is far beyond the ordinary limits of thought, 

 ranging from 125,000 particles of coarse sand to 

 15,625,000,000,000 particles of the finest silt in one 

 cubic inch. In other words, if all the particles in 

 one cubic inch of soil consisting of fine silt were 

 placed side by side, they would form a continuous 

 chain over a thousand miles long. The farmer, 

 when he tills the soil, deals with countless numbers 

 of individual soil grains, far surpassing the under- 

 standing of the human mind. It is the immense 

 number of constituent soil particles that gives to 

 the soil man}^ of its most valual)le properties. 



It nuist be remembered that no natural soil is 

 made up of particles all of which are of the same size ; 

 all sizes, from the coarsest sand to the finest clay, 

 are usually present (Fig. 17). These particles of all 

 sizes are not arranged in the soil in a regular, orderly 

 way; they are not placed side by side wath geo- 

 metrical regularity; they are rather jumbled together 

 in every possible way. The larger sand grains touch 

 and form comparatively large interstitial spaces 

 into which the finer silt and clay grains filter. Then, 

 again, the clay particles, which have cementing 

 properties, bind, as it were, one particle to another. 

 A sand grain may have attached to it hundreds, or 



