172 Classification a/ Soils 



3. It is difficult to associate each of the three clioseu groups with 

 distinct properties in regard to their relation to the movements of 

 water (49). 



4. Luxmore(2!i) has shown that many properties of soils can be 

 correlated witli the proportion of particles havinfj; a maximum diameter 

 of 0-01 mm. 



5. Takinf; into account the insensible degrees by which any given 

 type merges into another, are we justified in laying down limiting per- 

 centages for classes of soils? A soil with a given analysis behaving as 

 a sandy loam in a district of deficient rainfall becomes a loam with a 

 medium rainfall, and a heavy loam with a very high rainfall. The influence 

 of the amounts of organic matter and of calcium carbonate cannot be 

 ignored. 



6. Different analysts, working on the same sample of soil frequently 

 — as often as not — obtain discordant results for the clay and fine silt 

 fractions, though they will agree as to the total amount of these two 

 grades present. 



7. The rapidity with wliich a large number of samples can be 

 analysed if the determination of the clay is omitted is an important 

 point. 



8. The curves for the sunuuat ion percentages are better characterised 

 by the proposed limits. 



The various limiting diameters of the three classes are shown in 

 Table V. 



Table V. Classification of particles. 



Limits of diameters in millimetres 



. * , 



Coarse (sandl Medium (silt) Fine (clay) 



System Maximum Minimum Maximum Minimum Maximum Minimum 



American 20 005 005 OOOf) 0005 — 



Wilsdon 10 004 004 0002 0002 — 



Proposed 30 0-2 0-2 001 001 — 



[Or possibly — 0-2 0-2 0-02 002 — ] 



Atterberg (44) has suggested the limits -2, -02 and -002, and there 

 appears to be fairly strong evidence that a geometrical progression is 

 the type of classification required. As English analysts do not recognise 

 the hmit 0-02, the nearest English point (0-01) has been adopted here 

 provisionally. The result obtained wifh the types previously considered 

 is showm in Fig. 4. 



