. The elements of geology, for popular use : containing a description of the geological formations and mineral resources of the United States. Geology; Geology. 44 SLATE. GLAY. gray, red, and other colours. Common plaster of Paris has a laminated or granular structure, and is sometimes compact. It is softer than common limestone, and can be easily scratched with the nail. It does not efferversce with acids. Its con- stituent parts are, lime 32, sulphuric acid 46, water 31. There is a variety which contains no water, and is therefore called anhydrous. When crystal- lized, gypsum can be separate
. The elements of geology, for popular use : containing a description of the geological formations and mineral resources of the United States. Geology; Geology. 44 SLATE. GLAY. gray, red, and other colours. Common plaster of Paris has a laminated or granular structure, and is sometimes compact. It is softer than common limestone, and can be easily scratched with the nail. It does not efferversce with acids. Its con- stituent parts are, lime 32, sulphuric acid 46, water 31. There is a variety which contains no water, and is therefore called anhydrous. When crystal- lized, gypsum can be separated into thin plates, like mica and talc, which break into four-sided Fig. 6. cryStals, as in fig. 6. This mineral is used for various purposes, such as a ma- nure, for cements, castings, &c. It is generally found in connexion with salt- springs or rock-salt. Slate and clay.—By the term slate, when employ- ed alone, is understood clay slate, or what is some- times called argillaceous schistus, known generally by the name of roof slate, as it is used for that pur- pose. It consists of silex48, alumine 23, and some- times a little carbon, potash, water, and oxide of iron. It is easily scratched by the knife, and on moistening, by breathing on it, gives out a peculiar odour. Its colours are usually bluish, greenish, gray, or reddish. The slate rocks have generally a slaty structure, and may be split in two directions, which have an acute angle with each other; but some varieties cannot be split in any direction. On account of the potash contained in some species of slate, it is easily decomposed on exposure to the atmosphere, forming a clayey soil of great fertility. What is called shale by the English miners is only a soft, dark-coloured slate, containing more carbon than common slate. Slate is employed for roofing buildings, drawing slates, and pencils, and the clays for making bricks and pottery. The clays are of the same chymical composition as slate. Both are very abundan
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Keywords: ., bookcentury1800, bookpublishernewyorkharperb, booksubjectgeology
