BED

This article appears in Volume V03, Page 613 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: BEC-BER

BED , in geology, a

term

TERM

for certain kinds of

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

horizontal

HORIZONTAL

or very nearly so; when the upper and lower surfaces of a bed are parallel, the bedding is said to be 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

paper

PAPER
PAPER (Fr. papier, from Lat. papyrus)

, e.g.

paper

PAPER
PAPER (Fr. papier, from Lat. papyrus)

shales, such thin beds being often termed layers or laminae; intermediate regular varieties may be called flags, flagstones or tilestones. In 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 water or by the agency of wind; these are the " stratified " rocks.
The deposition. of rock material by moving water is not as613
a

rule

RULE

uniform, slight changes in the velocity produce an immediate

change

CHANGE (derived through the Fr. from the Late Lat. cambium, cambiare, to barter; the ultimate derivation is probably from the root which appears in the Gr. «a urmu', to bend)

in the size of the particles deposited upon a given area; thus a coarse 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

CHANGE (derived through the Fr. from the Late Lat. cambium, cambiare, to barter; the ultimate derivation is probably from the root which appears in the Gr. «a urmu', to bend)

in the nature of the contiguous strata; thus a

sandstone

SANDSTONE

is followed by a shale or vice versachanges which may be due to the varying volume or velocity of a current. Or the nature of the deposit may be influenced by chemical actiohs, whereby we get beds of rock-salt or gypsum between beds of marl. Or again, organic activities may influence the deposit, beds of coal may succeed layers of shale, iron-stone may lie between lime-stones or clays, a layer of large fossils or of flints may determine a bedding plane in massive limestones. Flaky minerals like 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 air) are trans-porting or depositing sand, &c., the bedding is generally not

horizontal

HORIZONTAL

, but inclined more or less steeply; this brings about the formation of what is variously called "

cross

CROSS

-bedding," "

diagonal

DIAGONAL (Gr. &a, through, ywvia, a corner)

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 process of weathering frequently produces an

appearance

APPEARANCE (from Lat. apparere, to appear)

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. H.)

End of Article: BED

If you wish, you can link directly to this article.

<a href="http://jcsm.org/StudyCenter/Encyclopedia/BEC_BER/BED.html">
BED
</a>

(Previous)
BECQUEREL

(Next)
BED (a common Teutonic word, cf. German Bett, p...

JCSM was founded in 1997 and exists to help the community and bring people into a life-changing and productive relationship with Jesus Christ. JCSM offers over 200,000 free web pages, including its weekly inspirational emails that were sent continuously for over a decade.

Jesus Christ Saves Ministries
P.O. Box 9297
San Diego, CA 92169
1-888-887-0417 or Email