I.] ANAL YSIS OF SOILS. 1 1 



13. These peaty soils therefore differ essentially 

 from the soils which have been produced by the 

 pulverization or powdering of rocks. Peat soils con- 

 sist almost entirely of vegetable matter, which often 

 reaches as much as 97 per cent, and they contain very 

 little mineral matter ; whilst soils produced from rocks 

 are chiefly composed of mineral matter, and have only 

 a small proportion of vegetable matter. 



14. For the convenience of being able to describe 

 with accuracy the character of soils, so that soils of the 

 same character may be called by the same names, it 

 has become necessary to classify soils according to 

 their texture and condition, as well as by their com- 

 position. The character is indicated by a mechanical 

 analysis, and the composition is determined by chemical 

 analysis. By these means we can inform ourselves with 

 great accuracy as to the composition and character of 

 any soil, and establish a regular classification. 



15. The mechanical analysis of soils is largely 

 based upon the proportions of clay and sand which they 

 contain. The term Clay is applied to the finer portions 

 of the mineral matter of the soil. These portions have 

 by various means become so reduced in size that they 

 are perfectly soft to the touch, and when pressed in the 

 hand retain the form into which they may be moulded 

 or pressed. The clay which is used for making bricks 

 and pottery is familiar to every one. It is soft, and 

 easily moulded in the hand, and when water is placed 

 in any hollow on its surface the water does not readily 

 soak away. 



1 6. Sand is just the reverse. It really consists of 

 very minute stones, and when pressed in the hand it is 

 gritty and hard to the touch. If any attempt be made 

 to mould it into any particular shape, it does not keep 

 the form so given to it. If a hollow be made on the 

 surface, and water be poured into it, the water quickly 

 passes through it. In the sand upon the seashore we 

 have a familiar example of the sand in soils. 



