An accessible introduction for geology enthusiasts,

local history buffs, and curious visitors.

Published on March 18, 2025 | Last modified on April 15, 2025

By Combe Martin History Project

Combe Martin History Homepage | Combe Martin Silver Mining

Combe Martin Industrial History

What makes Combe Martin's geology unique? Its rock formations, shaped during the Devonian Period, include slates with limestone beds that reveal ancient marine ecosystems.

Combe Martin’s breathtaking seascape and rich heritage are deeply intertwined, offering a unique glimpse into the town’s historical and geological significance. This accessible article includes a supporting  bibliography.

How Geology Forged Combe Martin’s Coastline and Community

Combe Martin's dramatic coastal landscape and the village's character were shaped by its geology, formed during the Devonian Period and sculpted by the Variscan Orogeny. 

The area features diverse formations: Hangman Sandstone, Combe Martin Slates and Limestones, and Morte Slates, yielding mineral wealth that fuelled the town's silver mining, limestone quarrying, and lime burning industries.

Explore Local Geological and Industrial Heritage

Combe Martin's jagged cliffs, hidden coves, and rocky shores are a testament to millions of years of geological activity. This includes erosion, 'faulting' and marine processes which all shaped the town’s distinctive geological and architectural character.

Beyond its horticultural legacy, the North Devon coastline has played a crucial role in the region's history, influencing its silver mining, limestone quarrying and burning, and maritime heritage.

Combe Martin is situated in an area of North Devon characterised by ancient Paleozoic rocks, primarily from the Devonian period. These rocks have been folded and faulted by compressive forces, as detailed in the British Geological Survey (BGS) Memoir for the Ilfracombe and Barnstaple area (1985).

Geological Formations of Combe Martin

The Combe Martin area consists of several distinct geological formations, each telling a part of the region's history:

• Hangman Sandstone: Known for its dramatic cliffs, the Hangman Sandstone is composed of thick-bedded sandstones formed during the Devonian period.

• Ilfracombe Slates: These slates, part of the Ilfracombe Formation, contain interbedded sandstones and limestone layers rich in marine fossils.

• Combe Martin Slates: This formation includes distinctive limestone beds like the Jenny Start Limestone, providing insights into ancient marine environments.

• Additionally, superficial deposits, known as drift deposits, influence the local terrain by covering the bedrock with layers of clay, sand, and gravel transported by natural processes.

A Guide for Newbies

This article, aimed at readers aged 13 and up, provides an accessible introduction to Combe Martin's geology, with a brief glossary and a bibliography at the end. A local map is included on this page.

We do not encourage unsupervised exploration of the local geology outdoors, which can be a dangerous pastime on the coast. There are published guidelines for exploring outdoors, including keeping to safe areas with experienced guides.

Official guidelines recommend prioritising your own safety, and that of the local environment.

Safety Guidelines

Always follow recommended safety guidelines when exploring geology outdoors. The coast, rocks and cliffs can be dangerous for everyone. Check tide schedules and be aware of potential rockfalls, dangerous paths and cliff edges, and slippery surfaces. Stay within your fitness levels and Be safe out there>  

The Ilfracombe Formation

The Combe Martin area's rock formations belong to the Ilfracombe Formation, which is divided into several members (listed in descending order):

• Kentisbury Slates Member

• Combe Martin Slates Member, which includes three distinctive limestone beds: Jenny Start Limestone, Combe Martin Beach Limestone, and David's Stone Limestone

• Lester Slates-and-Sandstones Member

• Wild Pear Slates Member

These sedimentary rocks were deposited in a shallow marine environment during the Middle Devonian period (approximately 388–383 million years ago).

Fossils found in the limestone beds, including corals (tiny sea animals that build hard skeletons) and brachiopods (marine animals with hard shells that resemble clams), help confirm this ancient environment (paleoenvironment).

Geological Structure Around Combe Martin

Evans (1922) discusses how Combe Martin's geological structure played a critical role in shaping the area's industrial heritage. The calcareous (chalky) slates, limestones, and quartz bands described in the region provided rich deposits of argentiferous galena (silver ore), which were extensively mined here.

Faults and fractures in the landscape concentrated ore veins, making certain areas highly productive. However, the resulting irregularity and unpredictability of these ore veins often hindered silver-lead mining in Combe Martin.

In summary, the unique geology of Combe Martin created both rich deposits and significant challenges for miners. The same geological faults and fractures that created concentrations of valuable ores also made finding and mining them much more difficult.

Combe Martin's geological wealth not only supported mining but also influenced other industries: lime burning and quarrying was central to the village's economy during medieval times and beyond ("The Geological Structure of the Country Round Combe Martin, North Devon" [Evans, J.W., D.Sc., F.R.S.], 1922).

The work of British geologist John William Evans CBE from 1922 remains relevant today, as it contributed to foundational geological understanding. While subsequent studies have refined and expanded upon his findings, many of his fundamental principles remain upheld in geological research.

His stratigraphic divisions of formations such as the Hangman Grits and Ilfracombe Beds, provided a detailed framework for understanding the area's geology. The work of Evans continues to inform modern geological research.

Combe Martin: A Village Shaped by Geology and Industry

Ongoing natural processes continue to influence the landscape, linking past and present. One of the longest main streets in Britain is lined by buildings showcasing local stone, local lime applications, cob earth constructions, and the local architecture.

Incorporating local stone, Combe Martin's old manor houses and buildings, some dating back to the medieval period, are tangible archives. They illustrate how geology influences human culture, building methods, and industry in the area.

Beneath the surface, mining tunnels reveal Combe Martin’s rich silver and lead mining legacy. Smelting, limestone quarrying and numerous lime-burning kilns also played a key role in the local economy.

In all, Combe Martin's polymetallic mining and geological heritage shaped the village’s development, influencing its landscape, economy, and buildings. Remnants and monuments to its industrial past can be visited today.

The Combe Martin Valley Fault is a significant geological feature that shaped the area's landscape, and influenced its silver and lead deposits.

The Hangman Sandstone Formation, part of the Devonian Exmoor Group, forms the imposing coastal cliffs, creating a striking escarpment along North Devon’s coastline and emphasising the region's complex geology.

Visit Combe Martin Museum and Information Point on Cross Street, and explore artifacts from the area's mining and quarrying past. Examine and magnify local rocks and fossils, in the museum's activity pod.

What Types of Rocks Are Found Here?

The geology of Combe Martin is characterised by several distinct formations; search the Lexicon of Named Rock Units database at the British Geological Survey.

1. Hangman Sandstone Formation: This formation consists mainly of thick-bedded, parallel laminated sandstones, often purple, grey, and green in color. 

• These sandstones, deposited during the Devonian period (Eifelian to Givetian), form the dramatic cliffs of Hangman Hill, including Great Hangman and Little Hangman.

• The sandstones are locally interbedded with cleaved shale, siltstone, and mudstone, and have undergone folding during the Variscan Orogeny [2][5][8].

2. Ilfracombe Formation: This formation is composed of slates with subordinate sandstones and limestones, exposed between Ilfracombe and Combe Martin. It includes several members:

• Kentisbury Slates Member: Alternating layers of slate-rich and sandstone-rich units.

• Combe Martin Slates Member, which includes the Jenny Start Limestone, Combe Martin Beach Limestone, and David's Stone Limestone.

• These limestones contain fossils of corals and brachiopods, indicating a shallow marine environment during the Middle Devonian period [1][7].

• Lester Slates-and-Sandstones Member: The sequence includes dark grey to grey slates, brownish-grey sandstones (some with cross-beds up to 1.4 m thick), gritty sandstones, siltstones, and mudstones.

• Wild Pear Slates Member: Heavily folded and cleaved silvery-grey slates. Some thin layers of sandstones, siltstones, and limestones, often rusty and iron-stained.

3. Morte Slates: Generally dark, fine-grained rocks shaped by heat and pressure over millions of years. However, the primary geological focus in Combe Martin is on the Hangman Sandstone Formation and the Ilfracombe Formation.

These formations have been significantly shaped by the Variscan Orogeny, a major mountain-building event that occurred during the late Carboniferous to early Permian periods, resulting in extensive folding and faulting in the area [1][7].

Citations:
[1] https://www.northdevon-aonb.org.uk/sites/default/files/users/ndaonb2/geo-hele-samsons-and-combe-martin-bays.pdf 
[2] https://wikishire.co.uk/wiki/Hangman_Cliffs 
[3] https://www.lyellcollection.org/doi/10.1144/gsl.jgs.1867.023.01-02.38 
[4] https://johnhmoore.co.uk/hele/geology.htm 
[5] https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=HGMS 
[6] https://data.jncc.gov.uk/data/f722dcd3-4cf1-46d8-9624-56abff537c8d/gcr-v16-fossil-fishes-of-great-britain-c7.pdf 
[7] https://geoscience.wales/wp-content/uploads/2018/09/Alan-Holiday-Variscan-Orogeny-Sept-2018.pdf 
[8] https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=HASA 

Devonian Geology and Coastal Evolution

Over millions of years, layers of sediment built up, forming the sandstones, siltstones, and limestones that we see today. These rocks were later folded and faulted by powerful Earth movements, creating the rugged cliffs and valleys that shape this landscape.

During the Devonian period (419–359 million years ago)—part of the Paleozoic Era, also known as the Age of Fishes—a variety of sedimentary rocks were deposited across this region. Mudstones and shales, formed from fine-grained sediment settling on ancient sea beds, are particularly abundant here.

Combe Martin’s oceanic climate, with frequent rainfall and coastal exposure, continues to shape these geological formations through ongoing weathering and erosion. This relentless process sculpts the dramatic coastline seen in our images.

The Rock Pools in Combe Martin 

In the rock pool image (above), the visible rock layers and formations of sandstone and limestone contribute to the physical structure that allows the rock pools to exist and determine their characteristics.

• These are directly related to the local geology in several ways.

• Formation from Rock Structure: The rock pools form because of the specific types and arrangements of rocks found in the area.

• The intertidal zone (submerged during high tide and exposed during low tide) consists of bedrock, and boulders of sandstone and limestone. These erode unevenly due to wave action and weathering.

• Natural depressions are created, trapping seawater and forming rock pools.

• Rock Type: The geology influences the chemical composition of the water in the rock pools, due to the rock interacting with the seawater and the different mineral compositions of the rocks.

• Habitats: The geology and rock pool formation provide habitats for a variety of marine species.

• There is a diverse ecosystem in these intertidal areas, including seaweed, barnacles, mollusks, and small crustaceans that thrive in this dynamic environment.

Combe Martin's Geological Faults and Fractures

Complex geological structures created a double-edged sword for Combe Martin silver mining. The folded and faulted terrain concentrated argentiferous galena in rich veins, making some areas highly productive. However, these same features led to irregular ore distribution.

• Folds are geological structures that form when rocks undergo gradual deformation. This process typically occurs deep beneath the Earth's surface, where rocks are subjected to intense pressure and elevated temperatures.
• Faults are geological discontinuities that occur when tectonic forces cause rock masses to fracture and shift relative to one another. These breaks in the Earth's crust are often associated with seismic activity, as the sudden release of built-up stress can trigger earthquakes.
• Faults and fractures acted as pathways for groundwater, leading to significant flooding in mine shafts and tunnels in Combe Martin. This persistent flooding issue was a major obstacle for silver mining operations in the area.
• Some mineral-rich deposits or veins were thick and rich in argentiferous galena, while others were thin, lens-shaped, or pinched out entirely.
• Irregular ore veins made mining operations inefficient and risky. Miners could spend significant time and resources excavating barren rock, or chasing veins that abruptly ended.

The Significant Combe Martin Valley Fault

The Combe Martin Valley Fault is an important geological feature that has shaped the landscape of the area. According to Douglas J. Shearman of Imperial College London (1967), this fault is a large crack in the Earth's crust that has moved the rocks on either side in two ways:

1. It has shifted the rocks sideways by about one and a half miles.

2. It has also moved one side up (or the other side down) by about 500 feet.

3. In contrast, the San Andreas Fault in the United States is a major continental fault that extends approximately 1,300 kilometres long, and about 25 kilometres deep, through California. 

4. The Combe Martin Valley Fault happened millions of years ago. It has played a crucial role in creating the valley and influencing the area's unique geology, including its silver and lead deposits.

5. Now inactive, the fault runs through Southwest England and is part of a larger system of cracks; its effects can be seen in the cliffs and shoreline around Combe Martin.

In summary, the Combe Martin Valley Fault has shaped the cliffs and valleys we see today, and thus plays a crucial role in the area's geology, mining history, and landscape formation. It is therefore an important feature for both scientific study and local heritage.

The Variscan Orogeny

The Variscan Orogeny resulted from continental collisions that formed the supercontinent Pangea by the late Palaeozoic, around 250 million years ago. This tectonic event caused extensive folding and faulting in the area, creating complex geological structures.

The assembly of Pangea is widely accepted to have occurred during the late Palaeozoic, specifically in the Carboniferous to Early Permian periods (approximately 359–250 million years ago).

One notable feature is a large fault running through Combe Martin Bay, with an estimated displacement of about 2 km. This fault, however, is of Tertiary age (approximately 66–2.6 million years ago). The Tertiary period is now divided into the Paleogene and Neogene periods.

The Variscan Orogeny in Plain Terms

The Variscan Orogeny created a vast range of mountains across Europe. These mountains stretched from Portugal and Spain through France, Germany, and into the Czech Republic.

Its effects are visible in Devon and Cornwall, where volcanic activity and granite formations occurred about 300–290 million years ago. Over time, erosion reduced these mountains significantly, and remnants of their geological features remain today.

Combe Martin's Limestone Beds

The limestone beds in the region contain fossil corals, and brachiopods (a class of crustaceans) indicating a shallow sea floor paleoenvironment (preserved in the rock record at some time in the past).

These fossils, particularly in the Jenny Start Limestone and David's Stone Limestone, suggest a Givetian age (Middle Devonian).

This rich fossil record provides valuable insights into the ancient marine ecosystems that once thrived in the Combe Martin area, during the Devonian period.

Combe Martin's High Water Table

Combe Martin’s geology, along with its location near the River Umber and water draining from nearby hills, results in a high water table. The local clay makes drainage difficult, increasing the risk of flooding. This has historically posed challenges for mining, especially in winter.

The high water table also affects local infrastructure, requiring careful management of drainage and sewer systems. It also shapes the area's ecosystem, influencing vegetation patterns.

While the raised water levels have to be managed, the high water table creates favourable conditions for wetland vegetation and supports species adapted to saturated soils.

Coastal Influence on Soil

Combe Martin's coastal location affects its soil through salt-laden air, diverse geology, and coastal erosion processes. The steep topography influences drainage, while the microclimate impacts soil temperature and moisture. Coastal vegetation and marine inputs also contribute to the soil's organic content.

While shale —fine-grained, clastic sedimentary rock— is present in the area, Combe Martin's soil is a complex mixture influenced by various geological and biological factors.

Geology of the Country Around Ilfracombe and Barnstaple (BGS, 1985) 

Key Points:

• This memoir provides a detailed geological overview of North Devon, covering formations, structures, and economic geology.
• Geological Formations: Includes the Ilfracombe Slates Formation (marine-origin slates, sandstones, and limestones), Baggy Sandstones Formation (sandstones and siltstones from marine and freshwater settings), and Pilton Mudstone Formation (shales and fossil-rich sandstones).
• The Ilfracombe Slates are layers of ancient mud and sand, once part of a seabed teeming with life. Today, you can still find fossils of those sea creatures in the rocks.
• Structural Geology: Examines folds, faults, and deformations shaping the region.
• Economic Geology: Discusses historical mining and the area's mineral resources.
• Edmonds, E A, Whittaker, A, and Williams, B J. 1985. Geology of the country around Ilfracombe and Barnstaple. Memoir of the British Geological Survey, Sheets 277 and 293 (England and Wales).

Fossil Crinoids in North Devon

A study by E. Głuchowski and G. Racki (2005) examined fossilised crinoid stems—marine invertebrates that resemble sea lilies—found in Devonian and Carboniferous rocks in North Devon. Crinoids are animals, not plants. 

The researchers identified several crinoid species, including one from Combe Martin and others from sites such as Baggy Point and Saunton Sands.

Their findings also highlight similarities with crinoid fossils from Europe, North America, and Asia, suggesting these marine animals were widespread in ancient oceans (Głuchowski & Racki, 2005. Proceedings of the Yorkshire Geological Society, 55(3), 161–170).

Why is This Crinoid Fossil Study Interesting?

The study is interesting because it reveals North Devon’s ancient marine life, connecting local marine invertebrate crinoid fossils to those found worldwide.

It helps scientists understand past ecosystems, species evolution, and geological changes while also being valuable for education and fossil enthusiasts.

Climate Change and Combe Martin's Geological Future

Climate change threatens Combe Martin's, and Devon's, coastal environment, intensifying erosion through rising sea levels and increased storm activity (Devon Climate Emergency, 2021).

Climate change poses threats to biodiversity and ecosystem health. Rising sea levels, erosion, and habitat loss are key concerns.

The North Devon Biosphere Reserve demonstrates sustainable practices by balancing conservation with community development, promoting knowledge sharing, and supporting local economies while protecting natural assets.

Combe Martin's Hangman cliffs face heightened risk from wave action and landslides, while altered sediment patterns endanger beaches and increase flood vulnerability. North Devon Council has published a Carbon, Environment and Biodiversity Plan>

Geological formations weaken due to changing weather patterns. Protecting this unique landscape for future generations requires coastal defences, managed retreat, identifying vulnerable areas, and community involvement. 

North Devon Biosphere

​The North Devon Biosphere's website serves as a comprehensive resource, dedicated to promoting the harmonious relationship between people and nature in North Devon.

It highlights the region's designation as a UNESCO Biosphere Reserve, emphasising the area's rich natural and cultural heritage.

North Devon's Biosphere Reserve is a UNESCO biosphere reserve, covering 55 square miles (140 sq. km).

The North Devon Biosphere highlights the increasing risks of coastal erosion, and the need for sustainable management in the region. Learn more at North Devon Biosphere>

Explore Further: Exmoor's Regional Geology

For a broader understanding of the geological context of Combe Martin, explore Exmoor National Park's "Exmoor's Geology" PDF. This document provides an overview of the Earth Science of Exmoor, including a geological map, a table of local rocks and fossils, and site suggestions for study.

South West Coast Path Geology Walks

For detailed information on Geology walks along the Exmoor and North Devon coast, including routes and geological highlights, visit the South West Coast Path website>

Conclusion

Combe Martin's geology is more than just an academic subject; it's an integral part of the village's identity and heritage. The rocks themselves provided the raw materials for local buildings and industries, most notably silver mining, while shaping the landscape.

Climate change threatens Combe Martin's, and Devon's, coastal environment. Mitigation through coastal defences, managed retreat, assessing which areas are most vulnerable to erosion and flooding, and community engagement, is crucial to protect this unique landscape for future generations.

The British Geological Survey memoir, Geology of the Country Around Ilfracombe and Barnstaple (1985), is a detailed and valuable resource for understanding North Devon’s geology.

The Combe Martin Valley Fault plays a crucial role in the area's geology, mining history, and landscape formation. It is therefore an important feature for both scientific study and local heritage.

In 2005, a study by E. Głuchowski and G. Racki examined fossilised crinoid stems—marine invertebrates that resemble sea lilies—found in Devonian and Carboniferous rocks in North Devon.

Research identified several crinoid species, including one from Combe Martin and others from sites such as Baggy Point and Saunton Sands.

Combe Martin's seaside location shapes its soil composition through marine air, varied geology, and erosion. The steep landscape and local clay affect drainage, while the oceanic climate influences soil conditions.

Coastal plants and sea-derived materials further enrich the soil's organic content.

However, the village's rocky landscape and seascape, its proximity to the River Umber, and the surrounding hills, also results in a high water table. This feature historically challenged mining operations, increased flood risks, and necessitates careful management of drainage systems today.

For comprehensive details on geology walks along the Exmoor and North Devon coast, including specific routes and notable geological features, visit the South West Coast Path website>

By understanding the geological history of Combe Martin—its Devonian rocks, evidence of ancient seas, and the legacy of the Variscan Orogeny—we gain a deeper appreciation of the forces that have shaped both the village and its people.

Text and images © Combe Martin History Project 2023-2026

Twelve Rules - Be Safe Out There

Prioritise safety on the coast by being aware of potential dangers, tides, and slippery rocks and surfaces. Here are twelve rules for safety when exploring the rocky areas of North Devon and Exmoor: 

1. Before setting out, inform others of your planned route and expected return time.

2. Consider exploring geology outdoors with experienced or qualified leaders.

3. Be aware of rapidly changing tides, potential rockfalls, and slippery rocks and surfaces. 

4. Dress appropriately for the terrain and weather: wear suitable clothing and stout footwear.

5. Be ready for changes in the weather, visibility, available light, and trail conditions.
6. If visiting coastal sites, check tide schedules to avoid being trapped by rising water levels.
7. Beware of dangerous cliffs, edges, and steep drops. These are common hazards in hilly coastal areas.
8. Local signs and waypoints, sheet maps, and digital maps, are essential tools for orientation.
9. Carry a first-aid kit and ensure someone in the group is trained in basic first aid.
10. A mobile phone and adequate signal are essential. Expect "dead signal" zones along the coast.

11. Follow Safety and Coastal Habitat Advice from the South West Coast Path organisation.

12. Avoid steps and paths down to beaches which are not maintained or appear dangerous.

Summary

Websites have a general duty of care, and this is not a definitive guide. By following Safety Advice from the South West Coast Path organisation, visitors can enjoy a safe and responsible exploration of Combe Martin’s fascinating geology.

Explore More

If you’re interested in fun geology activities, games, and quizzes, check out GeoMôn’s Kids’ Activities. The GeoMôn website provides a variety of educational materials, including a special section for children with interactive geology activities.

Learners may need supervision and should follow the safety guidelines.

Learners can also explore the Earth Learning Idea (ELI) website for even more exciting hands-on geology activities and experiments, bringing Earth science concepts to life in a fun and practical way.

GeoMôn’s Kids’ Activities features games, videos, quizzes, and hands-on projects aimed at sparking curiosity and enthusiasm for earth sciences among young learners.

It’s a great way to learn more about rocks, fossils, and the geological history of places like Combe Martin.

Glossary of Geological Terms

• Argentiferous galena: A mineral composed of lead ("led") sulphide (PbS) that contains silver (Ag). It's the most important ore of lead ("led") and a significant source of silver.

• Brachiopods: Marine animals with hard shells on their upper and lower surfaces. They are important index fossils.

• Carboniferous: A geological period that lasted from about 359 to 299 million years ago, characterised by vast forests and the formation of coal deposits.

• Clastic: Sedimentary rocks or particles that are composed of fragments of older rocks or minerals, such as sand, silt, or clay, which have been transported and deposited by natural forces.

• Combe Martin Fault: A significant geological fault in North Devon, formed by movements of the Earth's tectonic plates. It represents a zone of weakness in the Earth's crust and has played an important role in shaping the region’s geological history.

• Studying the Combe Martin Fault helps scientists understand past geological events, and the processes that have shaped the landscape

• Coral: Marine organisms that secrete calcium carbonate to form protective exoskeletons. Over time, coral colonies grow into vast underwater structures known as coral reefs.

• A notable example of coral is the Great Barrier Reef in Australia, the world's largest coral reef system.

• Devonian: A geological period of the Paleozoic era, spanning from about 419 to 359 million years ago, often known as the "Age of Fishes".

• Earthquakes: Intense shakings of the Earth's surface caused by the sudden movement of tectonic plates. This movement releases energy as seismic waves, causing the ground to shake.

• Earthquakes often occur along fault lines where these plates meet. They can also be triggered by volcanic activity or by human and industrial actions.

• Fault: A fracture or zone of fractures between two blocks of rock, which allows the blocks to move relative to each other. In other words, a Fault is a crack in the Earth's crust where two blocks of rock can move past each other.

• Fold: A curve or bend of a planar structure such as rock strata, bedding planes, or foliation in any type of rock. In other words, A Fold is a bend or curve in layers of rock. This happens when rocks are pushed or squeezed over time, causing them to bend instead of breaking.

• Fossils: The preserved remains or traces of plants and animals, that were buried in sand, mud, or other sediments under ancient seas, lakes, or rivers. They usually date back over 10,000 years.

• Hangman Grits Formation: Made up of tough sandstone layers, mixed with finer silt and mud deposits.

• Ilfracombe Formation: A geological formation in North Devon, consisting of alternating beds of sandstone and mudstone with occasional limestone beds.

• Igneous: Rock that solidifies from molten earth material is called igneous rock.

• Limestone: A sedimentary rock composed mainly of calcium carbonate (CaCO₃), often formed from the skeletal fragments of marine organisms.

• Metamorphosed: Rocks that have undergone transformation. A process involving heat and pressure that changes the mineral composition and texture of existing rocks.

• Neogene: The later of two geological periods of the Cenozoic Era, spanning from about 23 million years ago to the beginning of the Quaternary Period.

• Orogeny: A process in which a section of the earth's crust is folded and deformed by lateral compression to form a mountain range.

• Paleogene: The earlier of two geological periods of the Cenozoic Era, spanning from about 66 million to 23 million years ago.

• Paleozoic: An era of geological time spanning from about 541 to 252 million years ago.

• San Andreas Fault: While the Combe Martin and San Andreas (slicing California in two) faults are important geological features in their respective regions, the San Andreas Fault is a much larger and more significant structure in terms of its impact on plate tectonics and seismic hazards.

• Sandstone: This common rock type found in Combe Martin is made up of sand grains that have been naturally cemented together. It accounts for about 14% of all sedimentary rocks.

• Sedimentary Rock: Rock formed by the deposition and consolidation of sediment, usually in layered deposits.

• Siltstones: The creation of siltstone begins with the deposition of silt-sized particles by water, wind, or ice. Over time, these deposits are compacted and cemented, resulting in this sedimentary rock.

• Slates: Fine-grained, foliated metamorphic rock derived from an original shale-type sedimentary rock.

• Tertiary: An obsolete term for the geologic period from 66 million to 2.6 million years ago. Now divided into the Paleogene and Neogene periods.

• Variscan Orogeny: A geologic mountain-building event caused by the collision of tectonic plates during the late Paleozoic era. It formed the Variscan mountain belt across Western and Central Europe.

• Variscan regions include Portugal, Spain, Ireland, and areas of Britain including Cornwall and Devon.

Bibliography

Sources accessed March 18 to April 14, 2025

Allmon, W. D. (2023): Tertiary Period. Encyclopædia Britannica. Retrieved from https://www.britannica.com/science/Tertiary-Period/The-rise-of-mammals. 

BGS Lexicon of Named Rock Units: Ilfracombe Formation Description. Available at: https://webapps.bgs.ac.uk/lexicon/lexicon.cfm?pub=IFS.

Britannica (2025): Quartz. Encyclopedia Britannica. Available at: https://www.britannica.com/science/quartz.

British Geological Survey (BGS) (1993): Geology of the country around Ilfracombe and Barnstaple. Memoir for 1:50 000 geological sheets 277 and 293 (England and Wales). Available at: https://webapps.bgs.ac.uk/Memoirs/docs/B01666.html. 

British Geological Survey (BGS) (n.d.) Crinoids. Available at: https://www.bgs.ac.uk/discovering-geology/fossils-and-geological-time/crinoids.

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British Geological Survey (BGS) (n.d.) What is a rock? Available at: https://www.bgs.ac.uk/discovering-geology/rocks-and-minerals/. 

British Geological Survey (BGS) (n.d.): What causes earthquakes? Available at: https://www.bgs.ac.uk/discovering-geology/earth-hazards/earthquakes/what-causes-earthquakes/.

Combe Martin History and Heritage Project (2023-2025): Early silver mining in Combe Martin. Retrieved from https://www.combemartinvillage.co.uk/combe-martin-industrial-history/early-silver-mining-in-combe-martin.

Combe Martin History and Heritage Project (2025, February 10): Lime-burning and quarrying. Combe Martin Village. Retrieved from https://www.combemartinvillage.co.uk/combe-martin-industrial-history/lime-burning-and-quarrying.

Combe Martin History Project (2023-2025): Combe Martin Museum and Information Point. Retrieved from https://www.combemartinvillage.co.uk/community/combe-martin-museum. 

Combe Martin Museum (n.d.) Combe Martin Museum & Information Point. Available at: https://combemartinmuseum.co.uk/.

Devon Climate Emergency (n.d.): Flooding and Coastal Erosion Impacts. Available at: https://devonclimateemergency.org.uk/studies-and-data/climate-impacts-group-flooding-and-coastal-erosion/.

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