On the Analysis of Soils. 3Q 



dlftcrent climates, and under diflcrent circumstances. The 

 power of soils to absorb moisture, a principle essential to 

 their productiveness, ought to be much greater in warm 

 and dry countries than in cold and moist ones ; and the 

 quantity of fine aluminous earth they contain larger. Soils 

 likewise that are situated on declivities ought to be more 

 absorbent than those in the same climule on plains or in 

 valleys ~. The productiveness of soils must likewise be in- 

 fluenced by the nature of the subsoil, or the earthy or stony 

 strata on which thcv rest; and this circumstance ought to 

 be particularly attended to, in considering their chemical 

 nature, and the system of improvement. Thus, a sandy 

 soil may sometimes owe its fertility to the power of the 

 subsoil to retain water; and an absorbent clayey soil may 

 occasionallv be prevented from being barren, in a moist cli- 

 mate, by the influence of a substratum of sand or gravel. 



XVIII. Of the chemiral Cowpnsition of fertile Corn Soils 

 in the Climate. 



Those soils that are most productive of corn contain 

 always certain proportions of aluminous and calcareous 

 earth in a lincly divided state, and a certain quantity of 

 vegetable or animal matter. 



The quantity of calcareous earth is however very various, 

 and in some cases exceedingly small. A very fertile corn 

 soil from Ormislon in East Lothian aflforded me in a hun- 

 dred parts, only eleven parts of mild calcareous earth ; it 

 contained twenty- five parts of siliceous sand ; the finelv 

 divided clav amounted to forty-five parts. It lost nine in 

 decomposed animal and vegetable matter, and four in water, 

 and afforded indications of a small quantity of phosphate oi' 

 lime. 



This soil was of a very fine texture, and contained very 

 few stones or vegetable fibres. It is not unlikely that its 

 fertility was in some nieasure connected with the phosphate; 

 for this substance is found in wheat, oats, and barley, and 

 may be a part of their food. 



A soil from the low lands of Somersetshire, celebrated 

 for producing excellent crops of wheat and beans without 

 manure, I found to consist of one-ninth of sand, chiefly 

 siliceous, and eight-ninlhs of calcareous marie tinged with 

 iron, and containing about five parts in the hundred of ve^ 

 getablc matter. 1 could not deteet in it any phosphate or 

 sulphate of lime ; so that its fertility must liave depended 



' Kirwari. Trans. lr!bh Academy, vol v. p. 175. 



C 4 principally 



