DIFFERENT KINDS OF SOIL 23 



composed of clay and organic matter washed down 

 by the current. 



"The soil of heathy or shrubby land is composed 

 of fine sand and of humus from the decayed leaves 

 of heather and other plants. It is only used for 

 flower gardens, and furnishes an example of what 

 might be called sand-and-humus soil. 



"Clay is a soil which, when moistened with water 

 and thoroughly kneaded, becomes a soft and tena- 

 cious dough, suitable for molding into any desired 

 shape. When perfectly pure it is white, and is 

 known as kaolin, a rare substance of which porcelain 

 is made. Plastic clays are those that are unctuous 

 to the touch, forming with water a yielding mass that 

 hardens with firing. They are used in making pot- 

 tery. Smectite, or fuller's earth, is a clay of very 

 different character, not pliable when moistened, but 

 very absorbent of grease and hence used by fullers 

 for cleansing cloth of the oil left on it in weaving. 

 Ochres are clays colored either red or yellow by iron- 

 rust. They are used in coarse painting. Eed chalk 

 belongs to this class of clays. Marl is a mixture in 

 variable proportions of clay and limestone. Accord- 

 ing to which constituent predominates, it is called 

 argillaceous or calcareous. Subjected to the action 

 of air and moisture, marl becomes flaky and crumbles 

 to dust. Marl is used in agriculture to improve the 

 soil. 



"A clay soil is quite the opposite of a sandy soil: 

 water makes it swell and converts it into a sticky 

 paste which clings tenaciously to farming imple- 



