DEFINITIONS OP SOILS. 33 



which only is always the case as to silicious earth. Of this, in its 

 pare and tin combined state, as sand (capable of being separated by 

 washing in water), it requires a very large proportion, say not less 

 than 80 per cent, of the whole mass, to constitute a sandy soil. 

 But, in other soils, though consisting for much more than half their 

 mass of uncombined silicious sand, a much smaller proportion of 

 either one of the other earths would serve to make the latter the 

 predominant ingredient, and properly to give character and name 

 to the soil. Thus, from 35 to 40 per cent, of " purest clay" (which 

 itself contains about 60 per cent* of silica), or 30 per cent, of calx, 

 or 25 per cent, of humus, or perhaps less of each, under ordinary 

 conditions, would serve to constitute, respectively, either a clayey, 

 a chalky, or a humic soil ; though, in each case, the other and 

 much larger ingredients would be other earthy materials than the 

 one so predominating. 



But even in soils having some one physical ingredient sufficiently 

 predominant and distinguished to indicate their general character and 

 name, there also-are usually apparent the manifest though weaker 

 indications of the presence of some other influential ingredient. 

 For such compound qualities, terms may be compounded of the 

 foregoing, which will sufficiently express the characters referred to. 

 For this purpose, there will be found a convenience in using also 

 the term loam for all soils approaching to a medium texture and 

 composition of the two usually most abundant ingredients, silicious 

 sand and clay or soils in which the opposite qualities of silicious 

 and aluminous earths serve in great measure to correct each other, 

 leaving no great or injurious excess of either. Such a medium 

 texture, or soil approaching nearly to such, would be simply a loam. 

 If still more sandy, it might be termed a sandy loam ; or a clayey or 

 chalky, or peaty loam, under other conditions of physical constitu- 

 tion. Besides all these and other such compounded terms, others 

 may be used for other physical and accidental qualities of soils, as 

 stony, gravelly, ferruginous, &c., any of which may apply to any 

 soil of different predominant character, and different general de- 

 signation.* 



* The convenient and very common term loam is defined above (it is pre- 

 sumed) with enough precision and correctness ; and also in accordance with 

 common understanding. Yet this term offers (next, perhaps, to "marl") 

 one of the strongest examples of the conflict of definitions and confusion 

 which prevail among agricultural writers. This term is so common that it 

 is used by every one who writes of soils and which, in some one or other 

 sense, each writer probably considered as forming a very large, if not the 

 greatest proportion of the cultivated soils of his country, and of the world. 

 Some of various and contradictory and erroneous definitions will be here 

 quoted : 



Kirwan says "Loam denotes any soil moderately cohesive, and more so 



