Plymouth Sound, Shores and Cliffs is a Site of Special Scientific Interest (SSSI) around the

Plymouth Sound Plymouth Sound, or locally just The Sound, is a deep inlet or sound in the English Channel near Plymouth in England. Description Its southwest and southeast corners are Penlee Point in Cornwall and Wembury Point in Devon, a distance of abou ...

, a large area of water where the

River Plym The River Plym is a river in Devon, England. It runs from Dartmoor in the centre of the county southwest to meet the River Meavy, then south towards Plymouth Sound. The river is popular with canoeists, and the Plym Valley Railway runs alongsi ...

and Tamar meet. It stretches across the two ceremonial counties of

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. Devo ...

and

Cornwall Cornwall (; kw, Kernow ) is a historic county and ceremonial county in South West England. It is recognised as one of the Celtic nations, and is the homeland of the Cornish people. Cornwall is bordered to the north and west by the Atlantic ...

and the unitary authority area of Plymouth. It contains fossils of plants and sea creatures and its cliffs show a timeline of the Middle to Early Devonian period hundreds of millions of years ago

Geology

Lower to early Middle Devonian units of rock are visible from sections through the coastal cliffs and intertidal zones, which were laid down 417–354 million years ago. There are fossil remains of

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and ...

brachiopod Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, w ...

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a ...

, gastropods, rare

orthoconic An orthocone is an unusually long straight shell of a nautiloid cephalopod.; During the 18th and 19th centuries, all shells of this type were named '' Orthoceras'', creating a wastebasket taxon, but it is now known that many groups of nautiloids ...

nautiloid Nautiloids are a group of marine cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and '' Allonautilus''. Fossil nautiloids are diverse and speciose, with over 2,500 recorded specie ...

ostracod Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typi ...

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...

s, phacopids),

crinoids Crinoids are marine animals that make up the class Crinoidea. Crinoids that are attached to the sea bottom by a stalk in their adult form are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, which are ...

ostracoderm Ostracoderms () are the armored jawless fish of the Paleozoic Era. The term does not often appear in classifications today because it is paraphyletic (excluding jawed fishes) (may also be polyphyletic if anaspids are closer to cyclostomes) an ...

and

acanthodian Acanthodii or acanthodians is an extinct class of gnathostomes (jawed fishes), typically considered a paraphyletic group. They are currently considered to represent a grade of various fish lineages leading up to the extant Chondrichthyes, which ...

fish. Jennycliff Bay has steeply inclined folds, which flexure into open recumbent folds — some with

chevron Chevron (often relating to V-shaped patterns) may refer to: Science and technology * Chevron (aerospace), sawtooth patterns on some jet engines * Chevron (anatomy), a bone * '' Eulithis testata'', a moth * Chevron (geology), a fold in rock ...

form. The folds have developed cleavage in the slate and in the siltstones 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, although it is more widely spaced throughout the silt and sandstones. To the south, the cleavage dips at moderate low angles and the strata, which become overturned in places, dip steeply. The original direction of the strata can be established using the graded and cross-bedding of sedimentary structures. It demonstrates that the section is situated on the overturned, steep or northern limb of the Dartmouth

Antiform In structural geology, an anticline is a type of fold that is an arch-like shape and has its oldest beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex up in which the hinge or crest is the ...

, which can be traced from

Newquay Newquay ( ; kw, Tewynblustri) is a town on the north coast in Cornwall, in the south west of England. It is a civil parish, seaside resort, regional centre for aerospace industries, spaceport and a fishing port on the North Atlantic coast of ...

to Dartmouth. This is evidence a period of tectonic plate collision between 330 and 300 million years ago, which exerted pressure on the rock. Folds of three generations with cleavages are visible through the section in Bovisand Bay. Generally, the first generation folds have gently southern dipping limbs which are overturned or steep. The cleavage consistently dips about 40 degrees south. This indicates that this section has the Dartmouth Antiform passing through it. The far south consists of red and green slates with sandstones that were deposited in rivers and lakes. On the western flank (

), there are harder rocks such as Staddon Grit, which form a headland from Staddon Point. There are also deposits of sandstones in the shape of marine sand bars. Along most of the coast dramatic faults and folds in the rocks can be seen and, in some places, a chevron pattern is visible.

References

{{SSSIs Cornwall biological, state=collapsed Geography of Plymouth, Devon Sites of Special Scientific Interest in Devon Sites of Special Scientific Interest in Cornwall Sites of Special Scientific Interest notified in 1997 Geology of Devon Cornish coast