RELATION TO FERTILITY 17 



Hilgard always prefers to use a sample of the subsoil collected 

 immediately below the surface. The subsoil has moreover the 

 further advantage of being more uniform in character than 

 the surface soil. When humus is present, its total amount 

 should be determined in the sample prepared for analysis, 

 and the humus present in the various separated portions must 

 be deducted from their weight. Osborne states that boiling 

 has little effect in disintegrating the particles of a soil held 

 together by humates, and that rubbing with a caoutchouc pestle 

 is in this case distinctly preferable. The sum of the products 

 of the mechanical analysis of a soil generally exhibits a small 

 loss, due to the removal of soluble matter by the water. 



Relation of Physical Constitution to Fertility. We will 

 now proceed to give examples of the physical constitution 

 of soils, as determined by the more accurate methods just 

 described. Our first examples (Table I) shall be selected from 

 Hilgard's splendid series of analyses of the soils of Mississippi 

 (Proc. American Ass. Advancement Science, 1873). The soils 

 had been sifted through a 3-0 mm. sieve before analysis. 



The pipe-clay is an example of a very pure natural clay ; 

 it is seen to have a very simple composition, the two finest 

 groups of constituents making up more than 95 per cent, of 

 the whole. 



The clay subsoil No. i is of tertiary origin. It is a heavy 

 intractable soil on which water will stand for weeks. It is 

 very difficult to till, and yields good crops only in favourable 

 seasons, as it is injured both by drought and excessive rain. 

 The composition is simple, the three finest groups of particles 

 forming 84 per cent, of the whole. 



The clay subsoil No. 2 is of similar origin to No. i ; it is 

 however more easily tilled, and is a productive soil. The 







