Cotham Marble or Landscape Marble is a variety of

Rhaetian The Rhaetian is the latest age (geology), age of the Triassic period (geology), Period (in geochronology) or the uppermost stage (stratigraphy), stage of the Triassic system (stratigraphy), System (in chronostratigraphy). It was preceded by the N ...

(uppermost

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

) stromatolitic

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

from the Penarth Group, found in south

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

and southwestern

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

in the area around

Bristol Bristol () is a City status in the United Kingdom, cathedral city, unitary authority area and ceremonial county in South West England, the most populous city in the region. Built around the River Avon, Bristol, River Avon, it is bordered by t ...

, possibly extending to the south coast in east

Devon Devon ( ; historically also known as Devonshire , ) is a ceremonial county in South West England. It is bordered by the Bristol Channel to the north, Somerset and Dorset to the east, the English Channel to the south, and Cornwall to the west ...

. It is named after Cotham House in

Cotham, Bristol Cotham is an area of Bristol, England, about 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 east, a ...

. 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 reign of Queen Victoria, from 20 June 1837 until her death on 22 January 1901. Slightly different definitions are sometimes used. The era followed the ...

. 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, part of the Penarth Group. 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 ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, s ...

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 Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...

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