Elsevier Encyclopedia of Geology

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Figure 17 Stratigraphical charts of the Sergipe-Alagoas, Espirito Santo, Campos, and Santos Basins of the Brazilian eastern margin.

322 BRAZIL

and the microcontinent, the convergence of Sa

o Fran-

cisco–Congo, Amazonia, and West Africa between

630 Ma and 590 Ma led to the development of the

central and northern segments of the Tocantins Sys-

tem. The final collision between Rio de la Plata and

Amazonia led to the development of the Paraguay

Belt in the Early Cambrian.

Borborema Strike-Slip System and Associated

Features

The Borborema Strike-slip System in north-eastern

Brazil (Figure 10) comprises a gigantic Brasiliano

strike-slip deformation zone associated with two

south-verging fold–thrust belts, which were once con-

tinuous with the Nigerian, Hoggar, and Central Afri-

can provinces. A fan-like array of dextral shear zones

outlines elongated basement blocks, which corres-

pond to the various massifs delimited in the region.

These blocks are composed of Archaean, Palaeopro-

terozoic, and Mesoproterozoic rocks, covered by

Mesoproterozoic to Neoproterozoic supracrustals,

and intruded by voluminous Neoproterozoic gran-

ites. The metasedimentary units form schist belts,

which wrap around the basement massifs.

The west-north-west–east-south-east-trending Ser-

gipano Belt in the south-eastern portion of the

Borborema System is made up of a system of south-

south-west-verging folds and thrusts, involving an

Archaean basement and a package of Neoproterozoic

passive-margin to foreland strata. The thrusts of the

Sergipano Belt are rooted in a dextral transpressional

shear zone, which marks a Brasiliano suture, juxta-

posing a continental mass represented by the remain-

ing parts of the system to the north with the Sa

Francisco–Congo Plate to the south. In Africa, the

Oubanguides or Central African Belt on the northern

Figure 18 Palaeogeographical reconstruction of the South Atlantic in the Late Aptian, showing the location of the Walvis–Sa

o Paulo

Ridge, which acted as a barrier to free oceanic circulation, thereby creating conditions favourable to evaporitic (salt) deposition in the

central segment of the eastern margin. Modified from Chang HK, Kowsmann RO, Figueiredo AMF, and Bender AA (1992) Tectonics and

stratigraphy of the East Brazil rift system: an overview.

Tectonophysics 213: 97–138, with permission from Elsevier.

BRAZIL 323

border of the Congo Craton is an extension of the

Sergipano Belt.

Separated from the Sergipano Belt by a basement

high, the Riacho do Pontal Belt, comprises a pile of

south-verging nappes involving Archaean basement

and schists and quartzites of uncertain ages.

Peak metamorphism and the emplacement of syn-

tectonic granites are dated by U-Pb and other

methods at between 630 Ma and 580 Ma, whereas

Ar-

Ar dates obtained in some of the main shear

zones indicate cooling ages of between 580 Ma and

500 Ma.

Phanerozoic Sedimentary Basins

The Phanerozoic sedimentary record of Brazil

(Figure 11) reflects three distinct plate-tectonic set-

tings: the continental interior, where large Palaeozoic

sag basins and Early Cretaceous intracontinental rifts

are recognized; the passive margin, represented by the

eastern border of South America; and the transform

margin, represented by the Brazilian northern or

equatorial margin. The continental margins de-

veloped from Mesozoic times onwards in response

to the breakup of Gondwana and the spreading of

the Atlantic Ocean.

Palaeozoic Sag Basins

During the Ordovician, following the cooling of

Brasiliano–Pan-African orogenic systems, sedimenta-

tion started in the newly assembled western

Gondwana in large interior sag basins, namely the

Solimo

es (600 000 km

), Amazonas (500 000 km

Parnaı

ba (600 000 km

), and Parana

(1 400 000 km

)

basins (Figure 11). The stratigraphical records of

these long-lived basins are characterized by a layer-

cake arrangement, reflecting mostly shallow-marine

sandy–shaly deposition (Figures 12 and 13).

The major stratigraphical sequences are bounded by

inter-regional unconformities, which are coeval along

the basins (Figure 12), suggesting global control

mechanisms. The existence of precursor rifts in these

Figure 19 Tectonic evolution of the Brazilian equatorial transform margin. Modified from Falkenhein K and Martins-Neto MA (eds.)

(2003)

Equatorial Margin Project, Part 2: Sequence Stratigraphy, Turbidites, Tertiary Wrench, Petroleum Systems. Multiclient project with

Petrobras, Agip, Shell, Chevron Texaco, JNOC, ConocoPhillips, Encana, ElPaso, KerrMcGee, Statoil, Devon, Ouro Preto, Fundac¸ a

Gorceix-NUPETRO. Final report (unpublished).

324 BRAZIL

basins is still controversial. Some deeper-processed

seismic lines and gravity–magnetometry maps suggest

a steer-head geometry, with a rift basin beneath the

main sag (Figure 13).

Some authors have considered the Parana

and Acre

basins to be foreland basins, because of their pos-

sible relationships to accretionary processes along

the margin of western Gondwana (Figure 14). The

Acre Basin is the name for the eastern pinch-out of

the Peruvian sub-Andean Maran

on-Ucayali foreland

wedge. The Parana

Basin comprises three basin cycles:

an Ordovician–Silurian thermal sag; a Devonian–

Triassic foreland basin; and a Jurassic–Cretaceous

sag associated with the opening of the Atlantic

Ocean (Figure 15). Permo-Carboniferous glacial de-

posits and an enormous volume of Early Cretaceous

(137–128Ma) flood basalts also characterize the

Parana

Basin fill.

Continental-Margin Basins and Associated

Interior Rifts

The breakup of western Gondwana in the Early Cret-

aceous created the continental margins of South

America and Africa. During the Neocomian, Barre-

mian, and Aptian, rifting propagated from south to

north, generating the eastern Brazilian margin basins.

The north-west–south-east-orientated Brazilian equa-

torial margin opened later, between the Aptian and

the Albian, as a transform margin. In the continental

interior, Precambrian lineaments were reactivated to

form interior rift basins.

Eastern Brazilian margin basins The eastern margin

basins are classical passive-margin basins, comprising

three sequences, reflecting precursor rift, transitional

proto-oceanic, and thermal drift (Figure 16).

Figure 20 StratigraphicalchartsofthePara

-Maranha

o,Ceara

,andPotiguarBasinsoftheBrazilianequatorialmargin.Modified

from the Brazilian Petroleum Agency (Age

ncia National do Petroleo,ANP)homepageatwww.anp.gov.br

BRAZIL 325

Neocomian to Early Aptian rift-stage deposits

consist of basalts and continental siliciclastics, de-

posited in depocentres controlled by normal fa-

ulting in alluvial, fluvial, deltaic, and lacustrine

environments.

The Aptian transitional proto-oceanic superse-

quence, characterized by low subsidence rates,

marks the incursion of marine waters into the basin

system, and comprises coastal to shallow-marine car-

bonates and mudstones and thick evaporites (Figures

16 and 17). Salt was deposited in the central segment

of the eastern margin (from the Santos to the Sergipe-

Alagoas basins; Figure 11) in an evaporative basin

created by a volcanic barrier, the Walvis–Sa

o Paulo

Ridge (Figure 18).

The first-order drift package comprises an Albian–

Cenomanian retrogradational transgressive superse-

quence, a Cenomanian–Turonian maximum flooding

interval, and a Late Cretaceous–Holocene pro-

gradational regressive supersequence. Whereas the

transgressive supersequence is mostly carbonate, the

regressive supersequence comprises unconformity-

bounded third-order depositional sequences of turbi-

dite-prone lowstand systems tracts and siliciclastic

or, subordinately, mixed-carbonate transgressive

highstand systems tracts (Figure 17). Salt tectonics

(deformational structures in response to gravity

driving motion of salt layers) controlled the sediment

bypass and the main depocentres, as well as the archi-

tecture of the drift package (Figure 16).

The Campos Basin in the southern segment of the

eastern margin (Figure 11) contains approximately

85% of the recoverable hydrocarbon reserves in

Brazil, forming together with the adjacent Santos

and Espirito Santo basins the most prolific oil

province of Brazil.

Equatorial margin basins The Brazilian equatorial

margin evolved in four tectonosedimentary stages

(Figures19,20and21):Neocomianinteriorrift;Aptian

transtensional rift; Albian wrench; and Cenomanian–

Holocene drift with wrench reactivations.

Figure 21 Schematic geological sections through the Brazilian equatorial-margin (A) Barreirinhas and (B) Poriguar offshore basins.

Modified from the Brazilian Petroleum Agency (Age

ncia National do Petroleo,ANP)homepageatwww.anp.gov.br

326 BRAZIL

During the Aptian, after the development of the

Neocomian interior rifts, the connection between

the Central and South Atlantic oceans was initiated

by the nucleation of an east–west-trending mega-

shear corridor, which controlled the evolution of the

Brazilian and West African equatorial margins until

the full breakup in the Early Cenomanian. This dex-

tral transtensional corridor was made up of north-

west–south-east-orientated releasing bends, alternat-

ing with east–west-orientated transfer segments

(Figure 19). The releasing bends hosted a series of

frontal rifts, whereas the transfer segments evolved

as sets of en echelon oblique rifts and east–west-orien-

tated transfer faults. During the Albian, with the

establishment of oceanic spreading centres in the

north-west–south-east-trending releasing bends, a

series of east–west-trending transform faults nucle-

ated, among them the St Paul, Romanche, and

Chain transforms. The previously formed rifts were

partially deformed in the vicinity of the fault zones.

Carbonate sedimentation prevailed in the releasing

bends (Para

-Maranha

o, Barreirinhas, and Potiguar

basins), whereas syn-wrench siliciclastic sediments

locally accumulated along the east–west-trending

transfer segments. During the Late Cretaceous and

Tertiary, strike-slip displacements along the oceanic

fracture zones induced wrench deformation in the

distal portions of the basins. Tertiary wrenching

also triggered gravitational gliding in slope areas

(Figure 21A). Siliciclastic sedimentation prevailed

until the Early Eocene. Carbonate and mixed systems

dominated later, except in the Amazon Cone area

(see Figure 11), where a sand–shale package several

kilometres thick accumulated from the mid-Miocene.

Early Cretaceous interior rifts Interior rifts formed

during the Early Cretaceous in response to intraplate

stresses related to the opening of the Central and

South Atlantic oceans. The rift basins, the Potiguar

Basin onshore, and the Tucano-Reco

ncavo-Jatoba

and Tacutu rifts (Figure 11), display half-graben

geometry and are filled with continental siliciclastic

rocks (Figure 22).

Tertiary Rifts and Related Features

An episode of rifting, whose driving mechanism is still

unknown, affected the whole eastern margin of Brazil

at the end of the Eocene and beginning of the Oligo-

cene. Reactivation of the Early Cretaceous rift struc-

tures, basic to alkaline magmatism, and nucleation of

a series of small rifts along the Serra do Mar on the

south-eastern coast are the main manifestations of

this event.

Figure 22 Schematic geological sections through the (A) Potiguar onshore and (B) Reco

ncavo interior rift basins. Modified from the

Brazilian Petroleum Agency (Age

ncia National do Petroleo,ANP)homepageatwww.anp.gov.br

BRAZIL 327

Glossary

Craton An ancient platform, i.e. a stable portion of a

continent, not affected by Phanerozoic orogenies.

Cratons also are differentiated pieces of continental

lithosphere, characterized by a relatively thin crust

coupled to a mantle root, whose thickness can

reach up to 400 km.

Geochronological province Region in which a char-

acteristic geochronological pattern predominates

and dates obtained by distinct methods in different

rock units are coherent.

Platform Relatively stable portion of a continent, not

affected by a given orogenic event.

Shields Areas of the continental interior where

Precambrian basement is exposed.

Further Reading

Almeida FFM, Hasui Y, Brito Neves BB, and Fuck RA

(1981) Brazilian structural provinces: an introduction.

Earth Science Reviews 17: 1–29.

Almeida FFM, Brito Neves BB, and Dal Re

Carneiro C

(2000) The origin and evolution of the South American

platform. Earth Science Reviews 50: 77–111.

Bizzi LA, Schobbenhaus C, Gonsalves JH, et al. (2001)

Geology, Tectonics and Mineral Resources of Brazil: Geo-

graphic Information System and Maps at the 1 : 2 500 000

scale. Brası

lia: CPRM-Servic¸o Geolo

gico do Brazil.

[CD-ROM. Online at http://www.cprm.gov.br].

Brito Neves BB, Campos Neto MC, and Fuck RA (1999)

From Rodinia to Western Gondwana: an approach to

the Brasiliano–Pan African cycle and orogenic collage.

Episodes 22: 155–199.

Chang HK, Kowsmann RO, Figueiredo AMF, and Bender

AA (1992) Tectonics and stratigraphy of the East

Brazil rift system: an overview. Tectonophysics 213:

97–138.

Cordani UG and Sato K (1999) Crustal evolution of

the South American Platform, based on Sm–Nd iso-

topic systematics on granitoid rocks. Episodes 22:

167–173.

Cordani UG, Milani EJ, Thomaz FA, and Campos DA (eds.)

(2000) Tectonic Evolution of South America. 31st

International Geological Congress, Rio de Janeiro.

Heilbron M, Mohriak WU, Valeriano CM, et al. (2000)

From collision to extension: the roots of the southeastern

continental margin of Brazil. In: Mohriak WU and

Talvani M (eds.) Atlantic Rifts and Continental Margins,

pp. 1–32. Geophysical Monograph 115. Washington DC:

American Geophysical Union.

Matos RMD (2000) Tectonic evolution of equatorial South

Atlantic. In: Mohriak WU and Talvani M (eds.) Atlantic

Rifts and Continental Margins, pp. 331–354. Geo-

physical Monograph 115. Washington DC: American

Geophysical Union.

Mello MR and Katz BJ (2001) Petroleum Systems of South

Atlantic Margins. AAPG Memoir 73. Tulsa: American

Association of Petroleum Geologists.

Schobbenhaus C, Campos DA, Derze GR, and Asmus HE

(1984) Geologic Map of Brazil and Adjoining Ocean

Floor Including Mineral Deposits Scale 1 : 2 500 000.

Brasilia: Ministe

rio das Minas e Energia.

Tankard AJ, Soruco RS, and Welsink HJ (1998) Petroleum

Basins of South America. AAPG Memoir 62. Tulsa:

American Association of Petroleum Geologists.

Trompette R (1994) Geology of Western Gondwana

(2000–500 Ma). Pan-African–Brasiliano Aggregation of

South America and Africa. Rotterdam: Balkema.

BUILDING STONE

A W Hatheway, Rolla, MO and Big Arm, MT, USA

Introduction

Unlike most other materials available to early man,

stone was the most durable and could be stacked in

courses to make walls to support roofs and thereby

afford protection from the elements. Building stone

continues to be used, valued for its strength and for

aesthetic beauty purposes. Hence there is now and will

remain a market for the technical talents of geologists

capable of locating and selecting deposits of durable

and attractive building stone, and in scoping and

devising the environmental protection measures now

necessary in extraction of building stone.

Historic Use of Building Stone

Historically, building stone has been employed for a

wide variety of structural and load-bearing purposes

(Table 1) Facade use of building stone was popular in

the world’s cities from the very advent of the high-rise

building (about 1890) and this situation stimulated

328 BUILDING STONE

Table 1 Historic and modern uses for building stone

Use Historic Modern

Housing Generally structurally practical only to one

or two storeys

Replaced since mid-nineteenth century by brick and timber

frames with occasional stone facades

Fortifications Durable material; employed in massive,

protective wall

Replaced by reinforced concrete since 1900

Road/street

paving

Sole material for all-weather roads and

streets

Infrequently used and then only for aesthetic purposes;

replaced since 1940 by use of crushed stone in asphaltic

concrete

Towers Watch towers and lighthouses; thick-walls

required for stability and resistance to

attack

Replaced by reinforced concrete in order to meet cost of

construction labour

Water supply Traditional usage for aqueducts and for

canal linings

Largely replaced by iron and steel conduits by 1900; lately by

synthetic organics (plastics)

Sewers Stone replaced by brick in mid-nineteenth

century

Obsolete today due to leakage and high cost of emplacement

labour

Commercial

buildings

Mainly as facades Used as facades on steel-framed buildings up to ten or more

stories

Civil buildings Limited to two storeys or requiring massive

wall thickness

Restricted to facades, for aesthetic purposes

Mansions and

institutions

Preferred construction material for wealthy

patrons

Employed only for special esthetic reasons due to high costs of

placement

Houses of

worship

Traditional; thick-walled or with flying

buttresses

Now replaced with reinforced concrete, often with stone as

cladding

Monuments The preferred material Remains the preferred material

Fireplaces and

furnaces

Replaced by firebrick by ca 1840 for furnaces Remains popular for fireplace facing; now used in conjunction

with steel or ceramic flues

Wall dressing,

interior and

exterior

Seldom used as was trivial and unnecessary Now the prime use of building stone

Bounding walls Commonplace where rock outcrops are

exposed for quarry removal

Ongoing demand in conservation areas and national parks

Table 2 Attractions and qualities of natural building stone

Quality Nature Geological consideration

Durability When other than ‘weak’ rock, stone has been

conditioned by the attack of geological agents

and properties in preparation for its selection

and use today

Most potential physical/chemical degradation has

already occurred and the stone likely will be durable

in its intended construction or architectural use

Resistance to

abrasion

Necessary quality for stairs, walkways, and road and

drive paving

Choice generally relegates to crystalline igneous or

metamorphic rock type low in presence of micas

Variety of intact

dimensions

Generally a result of geological depositional

conditions of origin or of diagenetic or metamorphic

changes that promote jointing and fissility as a

result in natural separation into articulated blocks,

preferably in a rectilinear pattern

Generally the result of either or both:

1. Joint spacing in igneous or crystalline metamorphic

work

2. Foliation jointing in high-grade metamorphic rock

3. Fluvial rounding in high-energy stream regimes,

often associated with paleglaciation

Planarity or

flatness;

when so

selected

Considered ‘flagstone’ when length or breadth-to-

thickness ratio is equal to or greater than about 10:1

Influenced by fissility imparted by sedimentologic

(bedding) character or by metamorphically-induced

open foliation

Colour Generally a wide variety, to please the client Directly related to lithology and geological origin

Colour variability generally greatest in volcanic

terrain, such as Italy

Locating geologist should examine for absence of

reactive minerals such as iron pyrites

Texture To please the client; but selected to avoid unsightly

stains

Visible as a form of surface roughness

Directly related to lithology and geological origin

BUILDING STONE 329

great interest in the national geological surveys. Most

geological surveys produced serial sets of geological

technical monographs on building stone and these

books today are the most valuable published re-

ferences for those geological professionals who are

interested in building stone.

Geological Character of Building

Stone

Stone possesses several strong qualities, valued by

clients and architects and was so recognized in the

early textbook on Engineering Geology in which

Penning (1880) cautioned that:

‘‘In the selection of a stone, it is not merely in the testing

it by hardness, composition, and appearance, that judg-

ment should be displayed, but also in ascertaining the

conditions under which it lay before removal from its

position in the quarry.’’

These qualities (Table 2) have geological origins,

most effectively identified by professional geologists.

Geological Controls on Nature of

Building Stone

Geological conditions exert first-order control over the

kinds of building stone available within a given eco-

nomic radius for recovery. These controls are largely

Table 3 Basic geological controls over nature of building stone

Control Defined Geological considerations

Sedimentary rock Most varieties are unsuitable for use

as building stone when uniaxial

compressive strength exceeds

about 15 MPa

Rock younger than Cretaceous (as Tertiary

era) aged tends to be ‘weak’ and

unsuitable because of immature

induration (density)

High clay mineral content generally

promotes unsuitability by way of spalling

and deterioration in exposure to the

elements

Glacial ice-contact deposits Often represents ground rich in

durable and colour-lithologic

diverse specimens

Only the most durable rock survives the

glacial plucking and transport experience

Often excellent fireplace and pillar stone

Requires considerable experience and

labour in selection of useful individual

stones

Rock lying in tectonic shear zones Tends to be mylonitinised or otherwise

shear-damaged and therefore

excessively fissile

Generally damaged beyond potential

resistance to long-term exposure to the

elements in exterior applications

Pluton-bounding zones of foliation in

granitic rock

Lends itself well as a fall facing Often has a pleasing and useful foliation

character leading to slightly planar

dimension ratio

Pluton-capping rhyolites in post-Jurassic

terrains

Somewhat rare due to removal

by erosion

Generally durable in climatically-temperate

regions while exhibiting good planar

dimensions for wall facing

Streams and rivers draining tertiary

volcanic centres of moderately high

rainfall or subject to cloudburst-type

periodic events

Usually present as boulders of a

variety of colours and textures

Fluvial action destroys weak varieties and

delivers only the most durable specimens

for collection

Foliated metamorphic rock in general Foliated rock splits or rips well with

minimum to no application of

explosives

Tends to scar when removed and handled

by machinery; requires care in recovery

at quarries

High-grade metamorphic rock in general

(Gneisses)

Gneisses and migmatites generally

suitable only as having experienced

glacial action

As grain size diminishes to that of schist,

desirable building stone qualities

decrease; especially in the presence

of micas

Rock within the contact aureole of a few

hundred meters of intrusive igneous

bodies

Sometimes visually undetectable

cation exchange effects generated

by hydrothermal effects of intrusion

Best to place samples in the weather for

observation; best to use application of

wet-dry interludes of testing by laboratory

cyclic wetting, and drying

Aggregate pits servicing great urban

centers on the fringes of igneous-

metamorphic complexes

Pits will be located along modern

rivers and streams colocated with

Plio-Pleistocene to recent fluvial

deposits

Pits operating by suction dredging tend to

have a ‘bone pile’ of vertebrate fossil

bones

330 BUILDING STONE

Table 4 Geologic tasks in prospecting for building stone

Task Defined Considerations

Determine general nature of

stone desired

Nature of stone determines the likely

source geological formation(s) to

be prospected

Reduces the exploration task to identification of suitable

terrain in lands available for recovery

Determine the economic radius

for stone recovery

This defines the area of exploration Acquire medium-scale geological maps of the area of

economic consideration

Assess suitability of deposit to

produce stone of desirable

end-use qualities

1. Dimensions on initial recovery,

without treatment

Most stone undergoes physical/chemical adjustment to

stress-removal on excavation and in the new

environment of placement2. Durability as exposed in place, on

construction

Assess ultimate quantity of rock

available

Must recognise costs involved in

recovery site development

Quantity as affected by property bounds and stability of

cuts made to recover the stone

Evaluate means of removal of

stone

Cost of production of each cubic

meter of stone prepared for

shipment to market

Suitable rate of production must be balanced by lack of

unacceptable damage to the produced stone

Evaluate cost of production of

units of the stone (cubic

meter)

Placement of accumulated stone

produce between haul loads

Most stone today is palletised for unit-transport

packages of one cubic meter; avoids labour costs in

distribution to building sites

Evaluate cost of transport of

units of stone (cubic meter) to

market areas

Resting place for spoil accumulated

from stone removal and selection

for transport

Ideally removed periodically to the final disposal site, in

accordance with quarry closure plans or for sale as

off-site embankment or fill material

Assess unit-cost impact of

providing environmental

protection

Planning and permitting, and

meeting environmental

requirements of the permit

1. Control of sedimentation and dust

2. Post-closure land use

3. Implementing approved plan of closure of the quarry

Table 5 Types of stone masonry

Type Description Considerations

Ashlar Individual blocks of rock are cut or trimmed, Masons attempt to make use of a high percentage of

rock as delivered from the quarry, sized in

accordance with provisional specifications of

supplier’s contract, not necessarily of comparable

size or ratio

Broken: As placed, the joints are not

continuous

Small: When individual stones are less than

300 mm thick

Rough: Squared-stone masonry laid as ‘range’

work

Squared-stone Masonry in which individual stones are

roughly squared in layers and roughly

dressed on beds and joints

Distinction between Ashlar and Squared-stone is that

the latter generally is laid dry or with mortar spacing

being 150 mm or greater between surfaces of stones

Quarry-faced Stone facing is left untreated as it comes from

the quarry

Commonly jointed or bedded stone comes with iron or

manganese-stained natural planar surfaces

Cut-and-polished stone A relatively new market with durable stone

being sold mainly for interior use as flooring

and counter surfaces

Durable stone is recovered from ‘the ends of the earth’

and sold at high prices controlled by vendor-

tradesmen

Rubble Consists of stone unshaped by hand or

machine and placed in its unaltered

condition from the quarry

Applied mainly to river-run fluvial boulders previously

shaped by the stone-to-stone contact in transport

from outcrop to mined deposit

Also applies to informal recovery of naturally

discontinuous rock recovered from small quarries by

fairly intensive hand labour

Dressed rubble Some attention to rough sizing by manual

hammering

May be dressed by tensile-splitting of field-broken or

split surfaces

Range-work Exposed fact of individual stone is roughly

dressed

Laid in rough courses

Broken range-work Courses are not continuous throughout the

wall or face

Facilitated with joint-bounded rock blocks

Random-work, or

‘uncoursed rubble’

Unsquared stone without attempted regular

courses

Laid without attempt to achieve horizontal or

sub-horizontal levelling between individual courses

of stone

Coursed rubble Sometimes roughly shaped by hammer so as

to fit approximately

Unsquared stone levelled off at specific heights to an

approximately horizontal surface of each course

BUILDING STONE 331

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