47 



the form of clods. Loamy sand and sandy marl are considered as light 

 soils, which are characterized by being capable of forming clods when 

 moist. Sand is considered as a loose soil, which is incapable of form- 

 ing clods even when moist. To the class of shifting soils belong the 

 sand drifts and dunes. Tenacious soils are unfavorable for tree growth, 

 because, firstly, they ofi'er considerable resistance to the penetration of 

 roots and their ramification throughout the soilj secondly, the circula- 

 tion of air and moisture in such soils is greatly impeded. Conse- 

 quently, tenacious soils are either excessively moist or excessively dry. 

 They absorb water slowly, but in large quantities. The power of soils 

 to retain moisture is in direct proportion to their tenacity. So the 

 power of retaining moisture is the greatest in clay; next comes lime, 

 loam, and, finally, sand. 



(3) Fermeahility. — Permeability, or the capacity of the soil to diffuse 

 its moisture, is proportional to the size of the soil particles. It is the 

 greatest in sand, next in loam, lime, and least in clay. 



(4) Warmth. — The warmth of soil, or facility with which it absorbs 

 heat, depends, ii side from the atmospheric temperature, upon its color 

 and the quantity of moisture it contains. Clayey soils do not easily 

 raise or lower their temperature with the corresponding increase or 

 decrease of the atmospheric temperature — they are cold soils. Sandy 

 soils are very active and respond to even slight changes in the atmos- 

 pheric temperature — they are warm soils. 



(5) Depth. — The upper layer, which is penetratedby the roots, is spoken 

 of as the soil; from it the trees draw the mineral nutriments. What is 

 below the soil is considered as the subsoil, which may be of the same 

 nature with the soil or may differ from it. 



Depth of soil in sylviculture is rather a relative conception. Soils 

 which are shallow for one kind of trees may be considered deep when 

 applied to other kinds of trees. It depends altogether on the nature 

 and development of the root systems of the species. Each species, 

 then, could have its own classification of soils as regards their depth ; 

 but for practical purposes a general and uniform classification may be 

 adopted. The classification adopted by the experiment stations in Ger- 

 many, given below, may be recommended : Very shallow, up to 6 inches ; 

 shallow, from 6 inches to 1 foot; medium, from 1 foot to 2 feet; deep, 

 from 2 feet to 4 feet; very deep, over 4 feet. 



Deep soils are very favorable, even for species with shallow root 

 systems, for they can retain the moisture longer, while the moisture 

 conditions of shallow soils depends upon the nature of the subsoil. 

 Usually shallow soils suffer either from excess of moisture or from 

 drought. 



Vegetable mold tends to modify extreme differences of the soils. It 

 makes stiff soils less tenacious and binds loose soils; it warms cold and 

 cools warmer soils; it increases the depth of soil ; it is capable of hold- 

 ing large masses of waters, which it gives gradually to the lower layer; 



