SAND is the name given to any mine ral substance in a hard granular or pal verulent form, whether strewed upon the surface of the _ground, found in strata at a certain depth, forming the beds of rivers, or the shores of the sea. The silicious sands seem to be either original crystalline formations, like the sand of Ise:filly, in six-sided prisms, terminated by two six-sided pyramids, or the clibris of granitic, quartzose, or other primitive crystal line rocks, and are abundantly distribut ed over the globe ; as in the immense plains known under the names of downs, deserts, steppes, Landes, dc., which, in Africa, Asia, Europe, and America, are entirely covered with loose sterile sand. Valuable metallic ores, those of gold, pla tinum, tin, copper, iron, titanium, often occur in the form of sand, or mixed with that earthy substance. Pure silicious sands are very valuable for the manufac ture of glass, for making mortars, filters, ameliorating dense clay soils, and many. other purposes. Its chief uses are in com positions for pottery and glass, and some sands arc more and some less fusi ble, according to the various stones from which they may have originated. The size of the particles is of importance in these works. It is the wearing down of rocks by attrition, during the sub-marine state, or the advance and retreat of the ocean.
Sand drifts, or floods, are arrested by planting marum, or sea-bent, or the arundo arenania, and other plants, that take root in sand.
Sandstone is, in most cases, compos ed chiefly of fine grains of quartz, united by a cement, which is nearly or quite in visible. The cement is variable, and may
be calcareous or marly, argillaceons, or argillo-ferruginous, or even silicious. When silicious, sandstone resembles quartz. Some varieties are so hard as to give fire with steel, while others are fri able, and may be reduced to powder by the fingers. Some have a slaty struc ture, arising from scattered and insulat ed plates of mica, and are often called sandstone slate. Some sandstones con tain grains of feldspar, flint, and silieious slate or plates of mica. The mica is in considerable quantities in those friable sandstones which accompany coal. Some are so ferruginous as to form a valuable ore of iron, containing either an oxide or the carbonate of iron. Red sandstone is sometimes connected with coal. In the older formation it sometimes con tains metallic substances disseminated through the mass, or in beds or veins. Various organic remains occur in sand stone, among which are reeds, impres sions of leaves, trunks of trees, and shells, both fluviatile and marine. In seine of its varieties it is often known by the name of freestone, and is em ployed as a building-stone. In most cases, it may be cut equally well in all directions ; but some varieties naturally divide into prismatic masses. Some compounds are used as mill-stones. When porous, it is employed for filter ing water. Some are even used for whet stones.