45 



mineral substances in a sufficient quantity to meet the requirements of 

 forest vegetation. The important thing to know about the soils 

 devoted to sylviculture is the relative quantities of the principal 

 components of the soil, i. e., of saod, clay, limestone, and organic mat- 

 ter which the soil contains; for the proportion in which these are 

 mixed determines the texture of the soil, hence its physical properties. 

 A chemical analysis of the soil can not supply this information, nor 

 does the nature of the rocks give a clue, for the same rocks do not 

 always form similar soils, and the products of decomposition do not 

 always remain together; besides the soil formed from a rock varies 

 in its properties with the stages of disintegration. The principal com- 

 ponents of the soil can best be determined by mechanical analysis, 

 which is recommended whenever possible. But for purposes at hand 

 the timber investigator can attain good results by examining the soil 

 in the field in the following manner: Take a certain quantity of 

 soil, say a pound, and dry it thoroughly at approximately the tem- 

 perature of boiling water. The ditference in weight before and after it 

 was dried gives the amount of moisture. Crumble the dry soil into 

 powder, take a certain quantity of it and mix it with water while 

 stirring; let the mixture stand for a while and decant carefully the 

 turbid liquid. Eepeat this process several times until the last water 

 to be poured off becomes altogether clear. What is left at the bottom 

 of the vessel constitutes sand: dry and weigh it. The turbid liquid 

 contains clay, limestone, and organic matter. Add gradually to the 

 turbid liquid hydrochloric acid until it turns litmus j^aper red; filter 

 it well and dry the residue, which contains clay and organic matter. 

 Ignite the residue in order to burn the organic matter; the difference 

 in weight before and after it was ignited gives the amount of organic 

 matter, the rest constitutes clay. Adding together the weight thus 

 obtained for sand, clay, and organic matter and subtracting the sum 

 from the original weight of the part of the dry soil taken for analysis, 

 the amount of limestone is roughly determined. According to the 

 proportion in which the principal components are mixed, soils are 

 classified as sand, loam, clay, and lime. 



Sandy soils contain 75 per cent or more sand; the remainder is clay. 

 When clay constitutes from 15 to 25 per cent, the soil is called loamy 

 sand ; when the clay is found to be 10 per cent or less, the soil is con- 

 sidered as a sand. Loamy soils contain from 60 to 70 per cent of sand, 

 about 5 per cent of lime, 5 per cent of iron oxides, while the rest is made 

 up of clay. When the clay constitutes 40 per cent, the soil is considered 

 as loam ; when the clay constitutes 30 per cent, it is considered as a 

 sandy loam. 



Clayey soils are those which contain 50 per cent of clay and more. 

 When clay and loam are mixed half-and-half, the soil is called clayey 

 loam; but when clay constitutes more than 60 per cent, the soil is 

 considered as a clay. 



