Dartmoor National Park was established in 1951 and is synonymous to us all for its iconic granite Tors and clitter slopes of boulders. Though there are no fossils within the granite there is an interesting geology story as well as being the backdrop to the Jurassic Coast and English Riviera Global Geopark.
Haytor - Dartmoor National Park
National Parks
The development of the National Parks in the UK was first discussed over 200 years ago. In 1810 the English Romantic poet William Wordsworth wrote of the Lake District as a, "sort of national property in which every man has the right and interest, who has an eye to perceive and a heart to enjoy'. Over the coming years the British developed an increasing interest in the countryside as well as an increasing need to access space for healthy outdoor recreation because of industrialisation and urbanisation.
A key milestone in the development of National Parks was by John Muir a Scottish-born American naturalist, writer, and advocate of U.S. forest conservation. He is credited for the establishment of the US National Park movement. In March 1872 the US Congress and 18th President Ulysses S. Grant signed the National Park Protection Act into law making Yellowstone an area of 2.2 million acres the first National Park for all to enjoy its unique hydrothermal and geologic features.
By 1890 Yellowstone was joined by Yosemite National Park. The US National Park Service was created by President Woodrow Wilson 1916 and today they manages 423 areas covering more than 85 million acres in every state, the District of Columbia, American Samoa, Guam, Puerto Rico, and the Virgin Islands.
These areas include national parks, monuments, battlefields, military parks, historical parks, historic sites, lakeshores, seashores, recreation areas, scenic rivers and trails, and the White House.
Although the US concept for wilderness protection is different to the UK the notion of protecting valuable natural resources is shared.
National Park's and the establishing of a new UK Government Agency called the National Parks Commission was first recommended in 1945 in the preliminary Dower Report. This report distinguished that National Parks in England and Wales differed from other concepts in that the land would largely remain in private ownership.
This report would form the platform for the 1947 National Parks Committee known as the Hobhouse Committee named after the Minister of Town and Country Planning Sir Arthur Hobhouse. They would introduce the National Parks and Access to Countryside Act with the objective of creating a charter of rights for all lovers of the open air. The Peak District would become the first National Park followed by the Lake District, Snowdonia and in 1951 Dartmoor National Park.
Dartmoor National Park
Dartmoor National Park Authority was created in 1995 to conserve and enhance the Park’s natural beauty, wildlife and cultural heritage and promote opportunities for the public to understand and enjoy the special qualities of Dartmoor National Park. In 2021 they celebrated 70 years (see video below).
Dartmoor National Park is 368 square miles and almost 65% of this area is covered in granite making it the largest exposure of granite in Southern Britain. This granite was formed 280 million years ago during the Paleozoic's late Carboniferous and early Permian Period. These exposures of granite are marked by over 160 Tors on Dartmoor (see Dartmoor Tor Map).
The extent of the granite in the South West extends some 200Km from the Isles of Scilly to Dartmoor and is named after the old Latin for Cornwall, the Cornubian Batholith. A batholith is a large body of hot molten igneous rock known as magma that rises deep from within the Earth towards the surface of the Earth. A batholith intrudes into the pre-existing local country rocks in a melted form and then slowly cools becomes solidified as granite.
The Cornubian Batholith has a number of granite domes and smaller satellite stocks along the 200Km and is estimated to be 10 km in thickness.
It is believed to be the result of multiple intrusions of the Devonian and Carboniferous Shales, sandstones, limestones and lavas covering a time span from 295 million years to 270 million years. There are six major domes between Dartmoor, Bodmin Moor, St Austell, Carnmenellis, Land’s End, and the Isles of Scilly with smaller satellite stocks found at St Michael’s Mount, St Agnes, Cligga Head, Castle an Dinas, Kit Hill, Hingston Down and Hemerdon Ball.
Whilst the magma of the Cornubian Batholith was slowly cooling and crystallising beneath the Earth's surface several processes were happening.
The combination of heat and pressure altered the pre-existing county rocks into metamorphic rocks. These transformed rocks form a characteristic aureole adjacent the granite. This aureole is a zone or ring of contact metamorphism that surrounds the batholith intrusion.
As the magma cooled and was becoming granite there was considerable hydrothermal mineral deposits from the hot hydrothermal mineral-laden water as it vapourised or minerals began to be dissolved and collected into rock cavities. This mineralisation included tin, copper ore, arsenic, lead ore, zinc, tungsten, cobalt, bismuth, antimony, uranium and even gold. The presence of hydrothermal water also reacted chemically with the granite and began to weather the granite in a process of kaolinisation depositing china clay.
The Granite
The term granite is derived from the Latin for granum or grain and Dartmoor National Park has three types of Dartmoor granite. Firstly, contact granite contaminated by minerals from surrounding rocks. Secondly, blue granite which is fine grained and thirdly, tor granite. Tor granite is characterised by igneous megacryst's whose crystalline grain is much larger, known as "Giant Granite" and is composed of interlocking crystals of white orthoclase feldspar, clear quartz and shiny black flakes of biotite mica.
As you visit the Jurassic Coast or English Riviera Global Geopark and in the background you see the familiar back drop of Dartmoor's Tors this blog should provide a bite-size summary. Have fun visiting the Dartmoor National Park.