Mount's Bay
[3] The eastern side of the bay centred around Marazion and St Michael's Mount was designated as a Marine Conservation Zone in January 2016.
[5] After Gunwalloe Fishing Cove the cliffs have the softer look of Devonian Meneage Formations of greywacke and mélange, with erosion a problem either side of the naturally dammed ria of Loe Pool.
[6] With the exception of the harder Devonian dolerite and gabbro of Cudden Point, the low, eroding cliffs and beaches continue to Mousehole.
All, but Marazion to Penzance, are examples of bay dune systems which develop where there is a limited supply of sand trapped within the shelter of two rocky headlands.
The deposits indicate cyclical changes from wetland, to coastal forest, to brackish conditions have been occurring over the past 12,000 years as sea levels rose.
[11] Either side of Penzance, on the beaches at Ponsandane and Wherrytown, evidence of a 'submerged forest' can sometimes be seen at low tide in the form of several partially fossilised tree trunks.
[12] Divers and trawlers also find submerged tree trunks across Mount's Bay and the forest may have covered a coastal plain 2 to 5 kilometres further south than today.
[13] The samples of peat and wood around Penzance have been radiocarbon dated and indicate that the forest was growing from at least 6,000 to around 4,000 years ago when rising sea levels finally killed the trees.
Storms sometimes destroyed the barriers depositing sand and gravel over peat beds in Marazion Marsh, and in the foundations of many buildings in Wherrytown and Long Rock.
Very little of the Loe Bar shingle is locally derived (compared with nearby Gunwalloe beach material to the south) and the deposits have been tentatively dated as Eocene.
[14] The shingle coming from drowned terraces of the former river that flowed down the English Channel; the nearest onshore source is 120 miles (190 km) away in East Devon.
The 12 km2 (4.6 sq mi) site includes the sea around St Michael's Mount and tidal reefs such as the Greeb, near Perranuthnoe, and the Long Rock.
In August 1625 "Turks took out of the church of Munigesca in Mount's Bay about sixty men, women and children and carried them away captives".
Over three summers, from 1778 Thomas Curtis sank a shaft on the Wherrytown reef and then built a 20-foot high wooden tower with a dressed stone breakwater at the base.
Sir Arthur Russell, a leading mineralogist and mining historian A. K. Hamilton Jenkin visited the reef in the summer of 1956 and found a roughly circular depression in the rock, surrounded by large blocks of elvan which were intended for the breakwater around the shaft.
