CLASSIFICATION OF SOILS. 81 



lime was cither inert earth, or positively hurtful by its peculiar 

 mechanical action ; and that such soils, when highly fertile (as the 

 mud of the Nile, with its 25 per cent.), were so by aid of their 

 other useful ingredients, which enabled the soil to withstand the 

 evil operation of the greater portion of its lime. 



It is scarcely necessary to state that neither of the agricultural 

 earths applied to soil can serve as a manure (i. e., have any chemi- 

 cal action), when there is already enough of the same earth present 

 to have any mechanical action. And however useful each of the 

 earths may be if applied where its chemical action is deficient, it 

 would be as absurd in reasoning as useless in practice, to apply 

 sand to sandy, and clay to clayey soils, or lime to the chalky, or 

 vegetable matters to peaty soils. 



The foregoing definitions and explanations offer some materials, 

 or ground-work, for the classification of soils. But, greatly as that 

 is needed, it is not designed here to attempt the construction of a 

 proper general classification or nomenclature which 'would serve to 

 add another failure to those of all preceding writers on soils. But 

 as it is impossible to discuss the subjects to be presented for con- 

 sideration in this essay without the use and aid of some definite 

 terms, I will adopt, for present and provisional use, the following 

 general terms for soils, deduced from their respective predominant 

 or most operative physical ingredients, and which will have rela- 

 tion only to mechanical constitution, and such qualities and cha- 

 racters of soils as are generally indicated by their texture, and are 

 evident to the senses. 



In reference, then, to physical predominating ingredients only, 

 each of the agricultural earths above described, by its quantity, 

 .serves to make a different general character of soil which, accord- 

 ing to the predominant physical constituent earth, belongs to some 

 one of the following five classes or general divisions of soils : 



1. A silicious or sandy soil contains so large a proportion of 

 silicious earth, in the state of sand, as by its excess to give more 

 or less of the peculiar texture and mechanical qualities of that earth 

 to the soil. Thus, a silicious or sandy soil will show most strongly 

 such qualities as openness, looseness, want of adhesiveness when 

 wet, permeability, rapidity in drying, &c. ; such as are still more 

 strongly shown by pure silicious sand. 



2. An aluminous, argillaceous, or clayey soil contains such ex- 

 cess of aluminous earth, or purest clay, as will give to the soil the 

 qualities of adhesiveness and plasticity when wet, more or less of 

 obstruction to the passage or sinking of rain-water, great tendency 

 to shrink in drying, and to hardness when dry, &c. 



3. A chalky, or super-calcareous soil, whether made so by true 

 chalk, or by any other form of calx or carbonate of lime, from any 

 other source, contains an excess of that agricultural earth large 



