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BRECCIA

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Originally appearing in Volume V04, Page 482 of the 1911 Encyclopedia Britannica.

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BRECCIA , in See also:

PETROLOGY

petrology, the name given to rocks consisting of angular fragments embedded in a See also:

MATRIX

matrix. They may be composed of volcanic rocks, limestones, siliceous charts, See also:

sand-stones, in fact of any See also:

KIND (O. E. ge-cynde, from the same root as is seen in " kin," supra)

kind of material, and the matrix, which usually corresponds to some extent to the fragments it encloses, may be siliceous, calcareous, argillaceous, &c. The distinctive See also:

CHARACTER (Gr. xapareri7p, from xap&crew, to scratch)

character of the See also:

GROUP

group is the See also:

sharp-edged and unworn shapes of the fragments; in conglomerates the pebbles are rounded and See also:

WATER

water-worn, having been transported by waves and currents from some distance. There are many ways in which breccias may originate. Some are formed by See also:

ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary processes of atmospheric erosion; See also:

frost, See also:

RAIN (O.E. regn; the word is common to Teutonic languages, cf. Ger. Regen, Swed. and Dan. regn; it has been connected with Lat. rigare, to wet, Gr. 13pixeav)

rain and gravity break up exposed surfaces of See also:

rock and detach pieces of all sizes; in this way screes are formed at the bases of cliffs, and barren See also:

mountain-tops are covered with broken debris. If such accumulations gather and are changed into hard rock by pressure and other indurating agencies they make typical breccias. Conglomerates often pass into rocks of this type, the difference being merely that the fragments are of purely See also:

LOCAL

local origin, and are unworn because they have not been transported. In caves breccias of See also:

LIMESTONE

limestone are produced by the collapse of See also:

PART

part of the roof, covering the See also:

FLOOR (from O. Eng. flor, a word common to many Teutonic languages, cf. Dutch vloer, and Ger. Flur, a field, in the feminine, and a floor, masculine)

floor with broken masses. See also:

CORAL

Coral reefs often contain extensive areas of limestone breccia, formed of detached pieces of rock which have been dislodged from the See also:

SURFACE

surface and have been carried down the steep See also:

EXTERNAL

external slopes of the See also:

REEF (1)

reef. Volcanic breccias are very See also:

COMMON

common near active or See also:

EXTINCT

extinct craters, as sudden outbursts of See also:

steam See also:

bear fragments from the older rocks and scatter them over the ground. Another group of breccias is due to crushing; these are produced in fissures, faults and See also:

VEINS

veins, below the surface, and may be described as " crush-breccias " and " See also:

FRICTION (from Lat. fricare, to rub)

friction-breccias." Very important and well-known examples of this class occur as veinstones, which may be metalliferous or not. A fissure is formed, probably by slight crustal movements, and is subsequently filled with material deposited from See also:

SOLUTION (from Lat. solvere, to loosen, dissolve)

solution (See also:

QUARTZ

quartz, See also:

CALCITE

calcite, See also:

BARYTES

barytes, &c.).

Very often displacement of the walls again takes See also:

PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place, and the infilling or " veinstone " is torn apart and brecciated. It may then be cemented together by a further introduction of See also:

MINERAL

mineral See also:

MATTER

matter, which may be the same as that first deposited or quite different. In important veins this See also:

PROCESS

process is often repeated several times: detached pieces of the See also:

COUNTRY (from the Mid. Eng. contre or contrie, and O. Fr. cuntree; Late Lat. contrata, showing the derivation from contra, opposite, over against, thus the tract of land which fronts the sight, cf. Ger. Gegend, neighbourhood)

country , See also:

BRECHIN

Brechin See also:

Castle played a piominent part in the Scottish See also:

War of rock are mingled with the shattered veinstone, and generally f See also:

Independence. In 1303 it withstood for twenty days a See also:

SIEGE (0. Fr. sege, siege, mod. siege, seat, ultimately from sedere, to sit, cf. Class. Lat. obsidium, a siege)

siege in experience alteration by the percolating mineral solutions. Other crush-breccias occurring on a much larger See also:

scale are due to the folding of strata which have unequal plasticities. If, for example, shales and sandstones are See also:

bent into a See also:

SERIES (a Latin word from serere, to join)

series of See also:

ARCHES, COURT OF

arches, the sandstones being harder and more resistant will tend to crack, while the shales, which are. soft and flow under See also:

GREAT

great pressures, are injected into the crevices and See also:

SEPARATE

separate the broken pieces from one another. Continued See also:

MOVEMENT

movement will give the brecciated fragments of See also:

SANDSTONE

sandstone a rounded See also:

FORM (Lat. forma)

form by rubbing them against one another, and, in this way, a crush-See also:

CONGLOMERATE (from the Lat. conglomerare, to form into a ball, glomus, glomeris; so also the general term " conglomeration " for a miscellaneous collection of things, gathered together in a mass)

conglomerate is produced. Great masses of limestone in the See also:

ALPS

Alps, Scottish See also:

HIGHLANDS, THE

Highlands, and all regions of intense folding are thus converted into breccias. Cherts frequently also show this structure; igneous rocks less commonly do so; but it is perhaps most common where there have been thin bedded alternations of rocks of different character, such as limestone and See also:

DOLERITE (from Gr. SoXepos, deceptive)

dolerite, limestone and See also:

QUARTZITE

quartzite, shale or See also:

PHYLLITE (Gr. 40)XAov, a leaf, probably because they yield leaf-like plates, owing to their fissility)

phyllite and sandstone. See also:

FAULT (Mid. Eng. faute, through the French, from the popular Latin use of fallere, to fail; the originallof the Latin being replaced in English in the 15th century)

Fault-breccias closely resemble vein-breccias, except that usually their fragments consist principally of the rocks which adjoin the fault and not of mineral deposits introduced in solution; but many veins occupy faults, and hence no hard and fast See also:

LINE

line can be See also:

DRAWN

drawn between these types of breccia. A third group of breccias is due to movement in a partly consolidated igneous rock, and may be called " fluxion-breccias." See also:

LAVA

Lava streams, especially when they consist of See also:

RHYOLITE (Gr. peiv, to flow, because of the frequency with which they exhibit fluxion structures)

rhyolite, See also:

DACITE (from Dacia, mod. Transylvania)

dacite and some kinds of See also:

ANDESITE

andesite, may rapidly solidify, and then become exceedingly brittle. If any part of the See also:

mass is still liquid, it may break up the solid crust by pressure from within and the angular fragments are enveloped by the fluid lava.

When the whole comes to See also:

REST (O. Eng. rest, reste, bed, cognate with other Teutonic forms, e.g. Ger. Rast, Riiste, rest, and probably Gothic Rasta, league, i.e. resting or stopping place)

rest and cools, it forms a typical " volcanic-fluxion-breccia." The same phenomena are some-times exemplified in intrusive sills and sheets. The fissures which are occupied by igneous dikes may be the seat of repeated injections following one another at longer or shorter intervals; and the latter may shatter the earlier See also:

DIKE, or DYKE (Old Eng. dic, a word which appears in various forms in many Teutonic languages, cf. Dutch dijk, German Teich, Danish dige, and in French, derived from Teutonic, digue; it is the same word as " ditch " and is ultimately connected with the ro

dike rocks, catching up the fragments. Among the older formations, especially when decomposition has gone on extensively, these fluxion and injection-breccias are often very hard to distinguish from the commoner volcanic-breccias and ash-beds, which have been produced by weathering, or by the explosive See also:

POWER [WILLIAM GRATTAN] TYRONE (1797-1841)

power of super-heated steam. (J. S.

End of Article: BRECCIA

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