X 



SCIENTIFIC AGRICULTURE. 107 - 



tenacity than any other earth, and after being deprived of its 

 water by- heat, becomes hard. After being heated to red 

 clay loses its ductile properties, is insoluble in water, and is of 

 no use in the soil, urtil, by long action of the atmosphere, 

 moisture, and animal manure, it is changed to its former con- 

 dition. Clay does not effervesce with acids, unless it contains 

 lime or carbonate of iron : it requires a high degree of heat for 

 its fusion. Clay is often found in combination with gypsum. 

 There are several varieties of clay, of which we notice only a 

 few. 



Kaolin, or porcelain clay, is the purest and finest, and is 

 used in the manufacture of porcelain ware: it is of a yellowish 

 or grayish white hue, and is supposed to be formed by the 

 decomposition of feldspar. 



Pipe day ranks next to kaolin in fineness, and is of various 

 hues. 



B^le is a species of red clay, used in the manufacture of 

 brown earthern ware. 



Potter's clay is used for bricks and stone ware. 

 CLi'j iron ore contains carbonate and phosphate of iron, and 

 has been described under the head of iron. 



TEAT. 



"Peat usually consists of soluble and insoluble geine, with 

 a mixture of undecomposed vegetable matter and some earths." 

 It is usually limited to the colder parts of the globe: it results 

 mostly from the accumulation and decomposition of mosses, 

 but also from any other vegetable matters which become 

 mixed with it 



The lower stratum of peat beds decays, while the plants on 

 the surface continue to grow, thus adding new matter annually 

 until they attain the thickness, in some cases, of thirty or forty 

 feet. In tropical climates, the heat produces decomposition so 

 speedily that vegetables are resolved into their elements before 

 peat can be formed. 



