34 THE PRINCIPLES OF 



the two. Applied to stiff clay it mellows it ; applied to sand 

 it stiffens it. 



A large proportion of the soils of this country have origin- 

 ated from the decay of limestone rocks. All our chalk soils 

 are of calcareous character ; so are our mountain limestones, 

 magnesian limestones, oolitic limestones, and our marls and 

 marbles of various kinds. They all yield us calcareous soils ; 

 and in order to understand intelligibly and practically the 

 classification of soils, the series already given must be modified 

 by the introduction of the term " calcareous." For example, 

 we may speak of a calcareous clay, or a clay in which lime 

 is a feature. Schiibler considered that the presence of from 

 five to twenty per cent, of lime in a clay were the limits 

 within which it might be spoken of properly as a marl. 



A calcareous loam is a mixture of clay and sand in which 

 lime is a feature. Lastly, we may have a calcareous sand, or 

 sand enlivened and improved by calcareous matter. Lime pos- 

 sesses a function which neither comes under its properties as a 

 plant food, nor yet as a mitigator of the character of soil. It is 

 its power to facilitate the decay of vegetable matter. This 

 is a well-known attribute of lime in accordance with which 

 we are by order of the Privy Council obliged to bury infected 

 carcases of animals in quick-lime. We are aware that quick- 

 lime exercises a very great effect upon organic matter. Lime 

 by virtue of this property tends to exhaust soils of organic 

 matter. It is the base required in the process of nitrification 

 to seize upon newly liberated nitric acid. The nitrification of 

 nitrogenous matter existing in a state of organic combination 

 is one of the most recent and one of the most important facts 

 brought out by agricultural chemistry. Lime plays an im- 

 portant part in this process by promoting the oxidation of 

 nitrogenous matter, and then furnishing a base for combin- 

 ation with nascent nitric acid. Nitrate of lime is easily 

 washed through the soil, and a great deal of it passes away 



