পাতা:পদার্থবিদ্যাসার.djvu/১৭৯

168 Pup. I have heard that these earths are disposed in strata: is it so - Tut. Yes: the first layer is frequently a rich black mould, whic', yields sustenance to trees and vegetables; beneath this is often found a thick bed of clay, which surfishes materials for bricks, &c.; next are deposited vast beds of gravel, that are of use in numerous points of view ; underneath these are beds of limestories, &c. which frequently surround usines that cousain valuable metals; after these are found beds of coal, which is use. ful for burning in cold climates. These strala are not always found together; but this statement taay si: flige to slew their generał arrangement. Pup. Are aay reinarkable stones found classed sunder this head Tat. There is one called the Asbestos, which has he singular property of not being consumed when burnt in the five. Pap. What particular støttes come under the order of saline * Tot. Some of the principal ones are line. chalk, and marble; in sides many stones that are useful for building. Pup. Whal nse is inade of Iime ? Tut. The uscs of lime are numerous and important. It is used in forming inoriar for buildings; and it is so durable, that buildings are kilown nearly 2000 years old, where the liune is still as hard as the stoires which it cements. Lime is also used for agricultural purposes: when spread on the ground, it is supposed to destroy what is hurtful, and to give it the power of retaining moisture, which is beneficial. ' It is also employed in the refining of sugar, in the manufacture of soap, in the melling of iron, and for various other purposes. Pup, liow is clialk useful ? . ., , . • • •