PiivsicAi. Composition of Caim: Colony .Soils. 



85) 



ft will he iiotifcd from the above how great is the variety in tlu; 

 class names applied by different investigators to the several classes of 

 soil. But an even greater Aariety exists in connection with the group- 

 ing of the different grades of particles which go to mak(! up a soil, and 

 which, when they prepoTulerate, impart to the soils their special charac- 

 ter. .Such terms as medium sand, fine sand, silt and clay have been 

 used above ; not only do different investigators differ in the terms 

 which they thus employ for any one grade of soil particles, but very 

 frequently one and the same term has been applied to widely distinct 

 grades. Snyder, for instance, uses the term " fine earth " to indicate 

 that portion of the soil which passes through a sieve with openings 

 .', niDi. ill diaiiu'ttM-. and furtlier grades this fine earth as follows : — 



Medium sand 

 Fine sand 

 Very fine sand 



Silt 



Fine silt 

 Clay 



Diameter of 

 Particles. 

 •25 to •') mm. 

 •1 „ -1^5 „ 

 •05 „ -1 

 •01 „ •OS „ 

 •005 „ -01 „ 

 below -005 ,, 



This, it may be observed, is exactly the grading adopted in the Govern- 

 ment laborator}'^ here, and is also employed by the United States 

 Bureau of Soils,* but it is far from being in general use. Thus Wolff' 

 and .Schone designate as fine earth all the soil that passes througli a 

 sieve with holes '3 mm. in diameter ; Knop applies the same term to 

 that which passes a I mm. mesh sieve. Whitney and some other 

 American chemists generally take '2 mm. Hilgard and others, again, 

 take -}y nnn. 



There is an equally great variety in the methods of classifying 

 the several finer soil grades ; thus Wollny (vid'' " Experiment Station 

 Record," vi, p. 762) classifies the several grades as follows : — 



.Stones 



Coarse gra\el 

 Medium gravel 

 Fine gravel 

 Coai'se sand 

 Medium sand 

 Fine sand . . . 

 Coarse silt... 

 Medium silt 

 Fine silt . . . 

 Clay 



Diameter of 



Particles, 

 over 10 1 



to 10 



„ 5 



•0 



•25 



•1 



•05 



•025 



•005 



•0001 



1 



■o 



•25 



•1 



•05 



•025 



•005 



■' Except for tlie coalescinji of the " silt "' anil ••tine silt " into one i;ra<lo. 



