Cotham Marble or Landscape Marble is a variety of

Rhaetian The Rhaetian is the latest age of the Triassic Period (in geochronology) or the uppermost stage of the Triassic System (in chronostratigraphy). It was preceded by the Norian and succeeded by the Hettangian (the lowermost stage or earliest age ...

(uppermost

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

) stromatolitic

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

from the

Penarth Group The Penarth Group is a Rhaetian age (Triassic) lithostratigraphic group (a sequence of rock strata) which is widespread in Britain. It is named from the seaside town of Penarth near Cardiff in south Wales where strata of this age are exposed ...

, found in south

Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

and southwestern

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

in the area around

Bristol Bristol () is a city, ceremonial county and unitary authority in England. Situated on the River Avon, it is bordered by the ceremonial counties of Gloucestershire to the north and Somerset to the south. Bristol is the most populous city in ...

, possibly extending to the south coast in east

Devon Devon ( , historically known as Devonshire , ) is a ceremonial and non-metropolitan county in South West England. The most populous settlement in Devon is the city of Plymouth, followed by Devon's county town, the city of Exeter. Devon is ...

. It is named after Cotham House in

Cotham, Bristol Cotham is an area of Bristol, England, about 1 mile north of the city centre. It is an affluent, leafy, inner city suburb situated north of the neighbourhoods of Kingsdown and St Paul’s and sandwiched between Gloucester Road (A38) to the eas ...

. This limestone was used for ornamental purposes, particularly during the

Victorian era In the history of the United Kingdom and the British Empire, the Victorian era was the period of Queen Victoria's reign, from 20 June 1837 until her death on 22 January 1901. The era followed the Georgian period and preceded the Edwardia ...

. On cut and polished faces the stone has the appearance of a landscape, complete with ploughed fields, trees, and hedges.

Occurrence

The beds known as Cotham Marble form part of the Cotham Member of the

Lilstock Formation The Lilstock Formation is a geologic formation in England. It preserves bivalve, insect and other invertebrate fossils, as well as fossil fish of '' Agkistracanthus mitgelensis'' and the basal theropod dinosaur '' Newtonsaurus cambrensis'' dating ...

, part of the

. They occur as lenses within the upper part of the Cotham Member. The marble is widely but patchily developed within the Cotham Member in its outcrop that extends from Glamorgan in South Wales, through the Bristol area to the coast of southeast Devon. The lenses are typically between 3 and over 20 centimetres thick and are up to 3 metres across. Within each lens there is a basal convex upward layer from which the landscape rises. The 'hedge' layer is about 5 millimetres thick, marked at the top by many small bumps. The 'trees', arborescent structures, extend upwards from the hedge and are relatively constant in height at about 4–5 cm, although somewhat shorter near the lens edges. In most cases the lenses contain only a single layer of the landscape, but two, or exceptionally three layers may be developed, known as double and triple landscape marble respectively, each growing up from the crest of the underlying layer.

Formation

The formation of the unusual structures in Cotham Marble has been ascribed to a number of causes. The earliest explanations were all inorganic, including evaporitic deposition and the effect of gas bubbles rising through the sediment. The interpretation that Cotham Marble is a stromatolite of

algal Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

origin was first proposed in 1961 and since has been confirmed by later work.

Crazy Cotham

Although described as a variety of Cotham Marble, and often found in association with it, this limestone has a different origin. It consists of thin limestone flakes often set almost on edge within a sandy limestone. These are interpreted to have a mechanical origin as a form of mud-flake

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of di ...

Uses

The marble is too soft for external use and has been mainly used to produce ornaments for display and as inlay in furnishings, such as tables and chimney pieces.

References

{{Reflist

External links

*Cotham Marble at th
''Virtual Microscope''
website. Limestone Geology of England Geology of Wales Triassic geology Bristol