The Great Estuarine Group is a sequence of rocks which outcrop around the coast of the West

Highlands Highland is a broad term for areas of higher elevation, such as a mountain range or mountainous plateau. Highland, Highlands, or The Highlands, may also refer to: Places Albania * Dukagjin Highlands Armenia * Armenian Highlands Australia *Sou ...

Scotland Scotland (, ) is a Countries of the United Kingdom, country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a Anglo-Scottish border, border with England to the southeast ...

. Laid down in the Hebrides Basin during the middle

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

, they are the rough time equivalent of the Inferior and

Great Oolite Group The Great Oolite Group is a Middle Jurassic stratigraphic unit that outcrops in southern England. It consists of a complex set of marine deposits primarily mudstone and bioclastic ooidal and fine grained limestone, deposited in nearshore to she ...

s found in southern

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 ...

. This sequence of rocks was originally named as the ‘Great Estuarine Series’ by the

geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althoug ...

, John Wesley Judd in 1878. There are outcrops on the islands of Skye,

Raasay Raasay (; gd, Ratharsair) or the Isle of Raasay is an island between the Isle of Skye and the mainland of Scotland. It is separated from Skye by the Sound of Raasay and from Applecross by the Inner Sound. It is famous for being the birt ...

Eigg Eigg (; gd, Eige; sco, Eigg) is one of the Small Isles in the Scottish Inner Hebrides. It lies to the south of the Isle of Skye and to the north of the Ardnamurchan peninsula. Eigg is long from north to south, and east to west. With an ar ...

Muck Muck most often refers to: *Muck (soil), a soil made up primarily of humus from drained swampland Muck may also refer to: Places Europe * Muck, Scotland, an island * Isle of Muck, County Antrim, a small island connected by sand spit to Portmu ...

and

Mull Mull may refer to: Places *Isle of Mull, a Scottish island in the Inner Hebrides ** Sound of Mull, between the Isle of Mull and the rest of Scotland * Mount Mull, Antarctica *Mull Hill, Isle of Man * Mull, Arkansas, a place along Arkansas Highway ...

and on the

Ardnamurchan Ardnamurchan (, gd, Àird nam Murchan: headland of the great seas) is a peninsula in the ward management area of Lochaber, Highland, Scotland, noted for being very unspoiled and undisturbed. Its remoteness is accentuated by the main access ...

peninsula. It comprises a series of shales,

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...

s and

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

s of non-marine origin. The Group overlies the Garantiana Mudstone of the ' Bearreraig Sandstone Formation' and is itself overlain by rocks of the 'Skye Lava Group', erupted during the Palaeocene. The lowermost (and hence oldest)

unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete piece of action (or beat) in a theatrical presentation Music * ''Unit'' (a ...

of the Great Estuarine Group is the ‘ Cullaidh Shale Formation’. Overlying this is the ' Elgol Sandstone Formation', the type locality of which is to be found at the village of

Elgol Elgol ( gd, Ealaghol) is a village on the shores of Loch Scavaig towards the end of the Strathaird peninsula in the Isle of Skye, in the Scottish Highlands. Name According to tradition, its name derives from a battle fought with five ships by ...

on Skye. These sandstones are interpreted as being

deltaic A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more rarel ...

in origin. Above the sandstone is the ' Lealt Shale Formation', a unit in which

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s of creatures which lived in

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estu ...

lagoons abound. These include

mussels Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which ...

sharks Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorp ...

and plesiosaurs. The discovery of the first plesiosaur was made in 1844 by the geologist

Hugh Miller Hugh Miller (10 October 1802 – 23/24 December 1856) was a self-taught Scottish geologist and writer, folklorist and an evangelical Christian. Life and work Miller was born in Cromarty, the first of three children of Harriet Wright ('' ...

. The ‘Kildonnan Member’ of the Lealt Shale Formation contains

stromatolites Stromatolites () or stromatoliths () are layered sedimentary formations (microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). Th ...

and various

microfossil A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, ...

s such as dinoflagellates and

acritarch Acritarchs are organic microfossils, known from approximately 1800 million years ago to the present. The classification is a catch all term used to refer to any organic microfossils that cannot be assigned to other groups. Their diversity refle ...

s. The succeeding ‘Lonfearn Member’ consist of shales and thin shelly and oolitic

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 ...

s with

conchostracan Clam shrimp are a group of bivalved branchiopod crustaceans that resemble the unrelated bivalved molluscs. They are extant and also known from the fossil record, from at least the Devonian period and perhaps before. They were originally classifi ...

fossils. It has also yielded

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

footprints. At the next

stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostra ...

level the ‘ Valtos Sandstone Formation’ represents a further series of deltaic sandstones. Large

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an ad ...

concretion A concretion is a hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular ...

s commonly occur within this formation. They are post-depositional in origin with individual nodules reaching more than a metre in diameter and cutting across the

bedding Bedding, also known as bedclothes or bed linen, is the materials laid above the mattress of a bed for hygiene, warmth, protection of the mattress, and decorative effect. Bedding is the removable and washable portion of a human sleeping environm ...

. The ‘ Duntulm Formation' succeeds the Valtos Formation and is in turn succeeded by the ‘

Kilmaluag Formation The Kilmaluag Formation is a Middle Jurassic geologic formation in Scotland. It was formerly known as the Ostracod Limestone for the abundance of fossil freshwater ostracods within it. The Kilmaluag Formation is very fossiliferous, with ostracods ...

’, and then by the youngest unit of the Great Estuarine Group, the ‘ Skudiburgh Formation’.p337-342, Trewin, N.H. (ed) 2002 ‘’The Geology of Scotland’’. The Geological Society, London

References

{{reflist Geological groups of the United Kingdom Geologic formations of Scotland Bajocian Stage Bathonian Stage

See also

References