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BED

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Originally appearing in Volume V03, Page 613 of the 1911 Encyclopedia Britannica.
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BED , in See also:

geology, a See also:term for certain kinds of See also:rock usually found to be arranged in more or less distinct layers; these are the beds of rock or strata. Normally; the bedding of rocks is See also:horizontal or very nearly so; when the upper and See also:lower surfaces of a bed are parallel, the bedding is said to be See also:regular; if it is thickest at one point and thins away thence in every direction, the bedding is lenticular. Beds may be thick (5o ft. or more) or so thin as to be like sheets of See also:paper, e.g. paper shales, such thin beds being often termed layers or laminae; intermediate regular varieties may be called flags, flagstones or tilestones. In See also:fine-grained rocks the bedding is usually thinner and more regular than in coarser rocks, such as sandstones and grits. Bedding is confined to rocks which have been formed under See also:water or by the agency of See also:wind; these are the " stratified " rocks. The deposition. of rock material by moving water is not as613 a See also:rule See also:uniform, slight changes in the velocity produce an immediate See also:change in the See also:size of the particles deposited upon a given See also:area; thus a coarse See also:sand layer may be succeeded by a finer sand or a mud, or two sandy layers may be separated by a thin layer of muddy shale. Bedding is most often induced by a change in the nature of the contiguous strata; thus a See also:sandstone is followed by a shale or See also:vice versa—changes which may be due to the varying See also:volume or velocity of a current. Or the nature of the See also:deposit may be influenced by chemical actiohs, whereby we get beds of rock-See also:salt or See also:gypsum between beds of See also:marl. Or again, organic activities may See also:influence the deposit, beds of See also:coal may succeed layers of shale, See also:iron-See also:stone may See also:lie between See also:lime-stones or See also:clays, a layer of large fossils or of flints may determine a bedding See also:plane in massive limestones. Flaky minerals like See also:mica frequently assist in the formation of bedding planes; and the pressure of superincumbent strata upon earlier formed deposits has no doubt often produced a tendency in the particles to arrange themselves normal to the direction of pressure, thus causing the rock to split more readily along the same direction. Where rapidly-moving currents of water (or See also:air) are trans-porting or depositing sand, &c., the bedding is generally not horizontal, but inclined more or less steeply; this brings about the formation of what is variously called " See also:cross-bedding," " See also:diagonal bedding", " current bedding " or improperly " false-bedding." Igneous materials, when deposited through the agency of water or air, exhibit bedding, but no true stratification is seen in igneous rocks that have solidified after cooling, although in granites and similar rocks the See also:process of weathering frequently produces an See also:appearance resembling this structure. Miners not infrequently describe a bed of rock as a " vein," if it is one that has some economic value, e.g. a " vein of coal or ironstone." (J.

A.

End of Article: BED

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