PHYSICAL PROPERTIES OF SOILS 



179 



elongated or lath-like particles, while those of wind origin are 

 generally rounded. Figure 87 gives some of these differences, both 

 as to shape and size. The closeness of packing varies with the shape 

 of the soil grains. As a general rule, the more uniform the size 

 and shape the closer the packing under normal conditions. 



Fio. 87. (After Merrill.) A. Showing annular character of quartz psxrtirles in decom- 

 posed gneiss. B. Quartz granules from beach sand. C. Showing outlines of shreds of vol- 

 canir dust art Keen under the microscope. Hocks, Hock-Weathering and Soila, Merrill 

 (Courtesy Mafmillaa Co.) 



9. Arrangement of Particles. There is no definite arrange- 

 ment of particles in soil's. Coarse sands approacli more nearly uni- 

 formity than any others. Theoretically, there are two general form? 

 of packing or arrangement, the columnar, figure 8.8 A. and oblique, 

 figure 88B. If the soil particles were spheres and of uniform size, 

 the columnar arrangement would give 47.64 per cent of air space, 



