16 An Account of the Soil [pt. i 



very coarsest to the very finest. It is convenient to 

 make divisions for the purpose of analysis and investi- 

 gation, but we must not forget that they are entirely 

 arbitrary and have no existence in nature. In this 

 country the following grades are adopted: 



Diameter of particles 

 Stones Above 3 mm. 



Gravel . . . 

 Coarse sand 

 Fine sand 

 Silt 



Fine silt 

 Clay 



Between 3 and 1 mm. 

 ., 1 and 0-2 mm. 



0-2 and 004 mm. 



004 and 0-01 mm. 



001 and 0-002 mm. 

 Below 0-002 mm. 



The clay on the whole possesses a certain set of proper- 

 ties and the fine silt possesses a different set. Never- 

 theless one cannot sharply distinguish the clay from the 

 fine silt because a considerable amount of material 

 occurs on the border line, possessing some of the pro- 

 perties of both. Wherever the line is drawn some 

 material gets included with the clay that behaves rather 

 like fine silt, and other material is included with the fine 

 silt that is rather Uke clay. It is equally impossible to 

 draw a sharp distinction between the silt and the fine 

 silt on the one hand, and the silt and fine sand on the 

 other. Wherever limits were selected thev would still 

 be open to criticism, and the groups adopted in this 

 country might no doubt be improved upon. Neverthe- 

 less, so many analyses have now been made here by 

 this method that no change would be justifiable unless 

 some great fundamental advantage would be gained 

 therebv. 



The older chemists taught that soil is composed of 

 two earths: sand and clav. It is now known tiiat this 



