PHYSICAL PROPERTIES OF SOILS 15 



grade, as clay in heavy clay soils, and medium sand 

 in sandy soils. No soil, however, is comptosed entirely 

 of one grade. The clay particles are exceedingly 

 small ; it would take 5000 of the larger ones, if laid in 



FIG. i. Medium sand x 150. FIG. 2. Fine sand x 150. FlG. 3. Very fine 

 sand x 150. FIG. 4. Silt x 325. FIG. 5. Fine silt x 325. FIG. 6. Clay x 325. 



a line with the edges touching, to, measure an inch, 

 while it would take but 50 of the medium sand par- 

 ticles to measure an inch. 



5. Sand. Sand is any rock fragment ranging in size 

 between 0.5 and 0.05 mm. in diameter. There are 



