52 SOILS 



all its grains are large enough to be readily sepa- 

 rated and distinguished without a microscope. 

 The grains of sand are large because quartz is very 

 hard, almost as hard as diamond ; hence the grains 

 weather very slowly. Sand contains very little 

 plant food, since the spaces between the large grains 

 allow water to pass through very readily. The 

 chief value of sand in a soil is in making it mellow, 

 porous and warm. Mix a handful of sand with a 

 handful of stiff clay and note that the latter is made 

 much more workable, but less retentive of moisture. 



Clay is made entirely of very fine particles, so 

 small that a single grain cannot be seen without 

 a microscope. It would take 5,000 large grains of 

 clay laid side by side to measure an inch. Clay 

 may be made from any kind of rock, as silica, 

 limestone, mica and feldspar. \Clay is exactly 

 opposite to sand in its physical properties. Being 

 very small, clay grains sink but slowly in water, 

 so they are often carried long distances by streams 

 and lodge only when the current becomes sluggish.* 

 The sediment that settles to the bottom of a glass of 

 muddy water is mostly clay. Because it contains 

 so many very small spaces between the minute 

 grains, clay absorbs water slowly, but holds it 

 tenaciously. Hence it is adhesive and unmanage- 

 able when wet. Pure clay is a powerful cement. 

 Clay in a soil gives it body and richness and in- 

 creases its ability to hold water, but if a soil has too 

 much clay it is wet, cold and hard to handle. 



Silt is a name given to the grains of a soil that 

 are intermediate in size and in character between 

 sand and clay. It holds water well and is espe- 

 cially rich in plant food. For these reasons a soil 

 that contains a large proportion of silt is apt to be 

 mellow and productive. Most of the soils of the 



