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AGRICULTURE WITH CHEMISTRY. 13

of retaining moisture, though in a considerably less de- gree than clay. By the action 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, to ‘i 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.

c &

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 duétile and tenacious; and loses these properties by the action of fire.

SILI

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