ENGLISH AGRICULTURE. 29 



sold off the farm. They are continually being drawn or 

 washed out of the soil, and the soil is recouped partly by 

 the continual decay of mineral fragments in the soil, and 

 partly by the application of fertilizing substances directly 

 to the soil. The most important of these constituents of 

 plants may be named upon the fingers. First of all there 

 is phosphorous ; secondly, there is potash ; thirdly, lime ; and 

 then follow soda, magnesia, sulphur, iron, silica, and chlorine. 

 Those are the principal constituents of fertile soils ; and 

 if we must add to the list we shall have to pass from the 

 domain of what are called mineral constituents, and include 

 nitrogen, hydrogen, and carbon. 



If a soil is rich in phosphoric acid, potash, lime, magnesia, 

 sulphuric acid, iron, chlorine, silica, and in a substance which 

 cannot be classed with them, but which is equally important, 

 namely, nitrogen, then we have, to speak broadly, the chief 

 soluble constituents which are required for the building up of 

 plants. Very frequently silica is accorded a very prominent 

 place by examinees. It is difficult to see for why. No one 

 denies the importance of silica, but it is so abundant in all 

 soils that it is scarcely necessary to parade it before us as 

 a very important constituent of a fertile soil. We may take 

 its presence for granted. 



Leaving the consideration of the soluble matter, we have 

 in the next place five proximate constituents of all soils, 

 wherever found. We begin with clay, chemically described 

 as the hyd rated silicate of alumina. Clay appears to have 

 been produced by the crumbling down of felspathic rocks, 

 such as granite. Granitic rocks, felspathic rocks, and felspar 

 seem somewhat unpromising raw materials from which to 

 derive clays. The forces already mentioned have acted upon 

 them. The alkalies have been washed out and carried away 

 in a state of solution. The sandy or quartzoze element has 

 been detached by running water, and the silicate of alumina 



