28 AGRICULTURE ON THE PACIFIC SLOPE 



shrinks, but keeps the shape into which it has been 

 molded, as is seen in adobe bricks and unburnt 

 earthenware. When heated red-hot, it becomes hard 

 and cannot again be made pasty. These properties 

 make it very important in soils. 



Pure sands and silts are not sticky when wet, cannot 

 be permanently molded by hand, and are not hardened 

 by burning. 



Natural clays, which can be found almost every- 

 where, are of many colors, black, blue, green, yellow, 

 red, gray, and white. Black clays often turn white 

 in burning, while the other colors mostly turn to red or 

 reddish, like burnt brick. It is the iron in the clay 

 that causes these color-changes. 



Sandy, loam, and clay soils. Sandy soils are loose, 

 sometimes too much so, and easily crushed between the 

 fingers. But when they contain some clay, they are 

 firmer, the; sand grains being held together by the clay. 

 Such are the loam soils that farmers and gardeners 

 generally prefer, because they are easily worked and 

 are safest for crops. When soils contain too much clay 

 or fine silt, they are difficult to cultivate. They are 

 very sticky when wet, and when dry often become as 

 hard as stone. Such soils are called heavy, or on the 

 Pacific Coast, "adobe." 



All cultivated soils, then, consist of sands, silts, 

 clay, and humus. Some contain, besides, large amounts 

 of iron rust, forming "red" lands. 



