SUB-PROVINCES, CLASSES, SOILS AND TYPES 121 



character of the soil and purpose for which it is collected. In arid 

 regions sampling is frequently done to a depth of 10 feet, especially 

 for moisture determinations, while in humid regions 40 inches is 

 sufficient. The divisions are frequently made -in G-, i)-, or 12-inch 

 depths, regardless of any natural divisions in the soil. At the 

 Illinois Experiment Station the samples are taken with a l 1 /^- 

 inch auger to a depth of 40 inches. The samples are divided into 

 (a) surface soil, G% inches in depth, about as deep as plowed, 

 and representing an approximate weight of 2,000,000 pounds per 

 acre for the common clays, clay loams, silt loams, sandy loams and 

 loams; (b) the subsurface stratum, G% to 20 inches in depth, 

 twice the thickness of the surface and representing approximately 

 a weight of 4,000,000 pounds per acre; and (c) the subsoil, 20 to 

 40 inches in depth and weighing approximately G. 000, 000 pounds 

 per acre. Each of the three samples is put into a separate bag and 

 analyzed separately. 



Sands are the heaviest soils and peats and mucks are lightest, 

 the latter two being only half as heavy as the former. The weights 

 of the strata are given in the preceding table. 



These divisions do not always represent the natural strata in the 

 soil, but the depth of 20 inches is usually near the natural line of 

 change between subsurface and subsoil, and although there is no 

 change at 40 inches yet that is a very convenient point, since it gives 

 the three strata with a relative thickness of 1, 2, and 3. 



The sample should be composite, and this is much more im- 

 portant for the surface than either of the other strata, since it may 

 have been modified more or less by tillage or other treatment. At 

 the Illinois Experiment Station the surface sample is secured from 

 12 to 16 different borings at some distance apart, but all from the 

 same ten acres. The subsurface and subsoil are secured from G to 8 

 different borings. 



QUESTIONS 



1. Define a sub-province. 



'1. What is the basis upon which classes are made? 



3. What factors are taken into account in making soil types? 



4. What is the system of soil nomenclature as used by the Bureau of 



Soils? 



5. What is the significance of color in naming soils? 

 0. How are "on' 1 and " over '' used in naming soils? 



7. Define peats. 



8. Define deep, medium and shallow peat. 



9. Define peaty loams and mucks. 



