AGRICULTURE WITH CHEMISTRY. 13 



of retaining moisture, though in a considerably less de- 

 gree than day. By the adion of fire it becomes lime, 

 and returns again to the state of chalk, or calcareous 

 matter, by exposure to air. 



ARGILLACEOUS MATTER 



Forms not only a large portion of the surface soil of 

 most countries, but is also found in the mineral strata, ta 

 an immense depth. Argillaceous matter, or clay, is no 

 where found pure, is more or less adulterated with the 

 different earths, and with different materials; such as 

 mineral, vegetable, and animal substances. 



The purest clay contains upwards of sixty per cent, of 

 siliceous matter, or sand. 



Clay is the earth most retentive of moisture, by 

 which it becomes du(P-ile and tenacious ; and loses these 

 properties by the adion of fire. 



SILr 



