46 



Limy soils are those whicli contain over 10 per cent of carbonate of 

 lime. According to the proportion of lime found in tlie soils, they are 

 subdivided into : 



Marl soils, containing from 10 to 20 per cent of carbonate of lime. 

 Loamy lime, containing about 30 per cent of carbonate of lime. 

 Clayey lime, containing about 40 per cent of carbonate of lime. 

 Lime, containing about 50 per cent of carbonate of lime. 



Tliese are the x^rincipal classes of soil ; besides, there may be distin- 

 guished two other classes of soil, namely, humus and ferruginous soil. 

 Humus soil contains 20 per cent and more of vegetable mold. Ferrugi- 

 nous S' il contains from 10 to 25 per cent of iron oxide. It can be easily 

 recognized by its brown red color. 



The above classification, which is commonly used in European for- 

 estry practice, is useful because at once suggestive of the physical 

 proi)erties of the soil. 



PHYSICAL PROPERTIES OF SOIL. 



The physical properties of a soil of importance to sylviculture are 

 tho e which determine its moisture conditions. Upon the amount of 

 moisture in the soil depends the chemical activity of the soil, its tem- 

 perature, and the supply of water for the growth of the plant. With 

 regard to moisture, soils are classified by European foresters as follows: 



Wet, where water flows from the clod without pressure being applied. 



Moist, where water drops from the clod on pressure being applied. 



Fresh, where traces of moisture are felt by pressing a handful of 

 soil. 



Dry, where traces of moisture are not felt, but when rubbed the soil 

 does not resolve into dust. 



Arid, where on rubbing the soil crumbles into dust. 



The chief physical properties of soil are : 



(1) Hygroscopicity. — Hygroscopicity of soil, or the capacity with 

 which it absorbs and retains water, depends upon the fineness of the 

 soil particles and is, therefore, in direct proportion to the compactness 

 of the soil. The power of absorbing rain water is the greate'st in lime, 

 then comes clay, loam, and sand. The aqueous vapors of the atmos- 

 phere are best absorbed by clay, next by lime, loam, and sand. 



(2) Tenacity. — Tenacity, or the degree of cohesiveness between the 

 particles of the soil, depends npon the size of the particles. Clay and 

 sand represent in this respect two extremes. The first one, consisting 

 of very fine grain, represents the most tenacious, while the latter, con- 

 sisting of granular and coarser grain, represents the least tenacious 

 soil. With regard to tenacity the soils may be classified as heavy, 

 mild, light, loose, and shifting. To the class of heavy, stiff, or tena- 

 cious soils belong clays, clayey loams, limes, and marls. Heavy 

 soils are characterized by the deej) cracks they form when suddenly 

 dried. To the class of mild soils belong loams, sandy loams, and loamy 

 limes. Mild soils crack when suddenly dried, but are able to retaia 



