AAPG’s Managing Editor of Digital Kelsey Kosh took Explorer readers to Ireland in the most recent edition. In celebration of St. Patrick’s Day, we’ll join in the exploration of the Emerald Isle with the help of my colleague at Howard Community College, geology professor Jennifer Kling. Kling has taken students to these locales on several study-abroad trips.
Sharon Lyon
Editor, GeoLifestyle
The Cliffs of Moher
Burben/ Shutterstock.com
The Cliffs of Moher are spectacular vertical cliffs that run along the southwestern edge of County Clare, overlooking the Atlantic Ocean and the Aran Islands. The cliffs are one of the most-visited tourist sites in Ireland.
Geology of the cliffs:
Extending about 9 miles, the cliffs rise more than 700 feet at their highest point. They are named after a now-demolished fort known as Mothar or Moher, which stood on Hag’s Head, the southernmost point.
Beds of Carboniferous-age sedimentary rocks (straddling the boundary between the Mississippian and Pennsylvanian) form the cliffs.
The lighter-color layers forming narrow ledges are sandstones, and the darker layers are siltstones and shales.
Accessible sandstone ledges contain trace fossils of worm trails, burrows, and casts.
An ancient river deposited sand, silt, and clay into a deepwater delta. The layers represent cyclothems, repeated deltaic sequences separated by thin marine bands.
The marine layers contain goniatite (ammonoid cephalopod) fossils, aiding correlation across the area.
Erosion by wave action undermines the cliff base and is causing collapse. Sea caves, sea stacks, and a sea arch are evidence of the formations' past extent.
For the birds: The area has been designated a Special Protection Area for birds, including puffins, razorbills, kittiwakes, and peregrine falcons.
How to visit:
Start at the Visitor Centre, which has exhibits covering the cliff’s geology, history, flora, and fauna. Watch the video of underwater caves below the cliffs.
Then, hike along the official walking path, but check open options first. A coastal walking trail was closed in February 2025 due to safety concerns.
Fun fact: The cliffs were used in the filming of the fifth Harry Potter movie as the setting for the Horcrux cave.
Kling’s comments: “Unlike in the United States, there are no railings, ropes, or barriers along much of the cliff. Instead, you stare uninterrupted along the cliffs and out into the Atlantic Ocean, and it is easy to understand how generations of Irish poets and artists gained inspiration from this view.”
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The Derreenavoggy Coal Mine is located in the Arigna Valley, 11 miles north of Carrick-on-Shannon. These mines were active from the 1700s to 1990.
Geology of the area:
The coal beds are upper Carboniferous in age, informally known as the Coal Measures.
The coal horizons are layers within a complex of sandstones, siltstones, and mudstones, which formed in a deltaic setting.
The coal seams are only a few feet thick, so miners had to work by hand, lying on their sides, inside a cavity only as thick as the seam.
The Derreenavoggy Mine site includes the largest spoil heap piles in the district, demonstrating both the scale of mining and the degree of unwanted rock that had to be processed to extract coal.
The rock face is preserved to show the sequence of the strata.
Kling’s comments: “It’s difficult to believe that miners worked the thin seams of this deposit. On the tour, we were invited to hunch down and try to fit into an area the size of the coal seam, and it was impossible to squeeze in—let alone imagine lying there for hours.”
Trip tips:
Strap on a hard hat and take the 45-minute mine tour led by an ex-miner.
Bring a jacket as the temperature is always 10° C (50° F).
The Visitor Centre preserves the area’s 400-year coal mining heritage with recordings, documents, photographs, and mining equipment.
Cliff face with chevron folds at Loughshinny; Courtesy of Jennifer Kling.
Loughshinny is a small coastal village about nine miles north of Dublin, known for its zigzag, chevron-folded rocks. The folds have angled hinges, with the northern limbs overturned.
Geology of Loughshinny:
In the early Carboniferous period, Ireland was covered in a shallow sea.
The vast Dublin Basin was filling with layers of calcareous mud and sand.
This shallow tropical sea was full of life, as evidenced by fossils of coral and crinoids in the beach rocks at Loughshinny.
The Variscan Orogeny, caused by the plate collision of Euramerica and Gondwana between 280–380 million years ago, buckled the soft sedimentary rocks into compression folds. This orogeny completed the assemblage of the Supercontinent of Pangea.
The dark layers within the folds are fine-grained mudstone. Lighter layers are somewhat coarser. The entire sequence is calcareous, with many calcite veins.
In addition to the spectacular folds at Loughshinny, the sandy beach is littered with lugworm mounds and ripple marks, making it an excellent classroom setting for lessons on trace fossils and depositional environments.
Trip tips:
The folded cliffs are easy to access, but you should visit at low tide.
If you look carefully, you can see the folds as a section in the cliff face and in plane-form on the foreshore platform.
Stop nearby: North of Loughshinny is Smugglers’ Cave, an old copper mine dating back to the 1800s.
Dig deeper: Learn more about Loughshinny’s history here.
Stop Here for a Post-Adventure Beer
A beer at Sean's Bar; Courtesy of Jennifer Kling
Located in Athlone, a central hub between all of these geologic locations, Sean’s Bar is in the Guinness Book of Records as Ireland’s oldest pub.
Fun facts:
The bar dates to 900 A.D. when an inn was built close to a great ford on the River Shannon.
During renovations in 1970, the walls of the bar were found to be made of “wattle and wicker,” and old coins were found within the walls.
When you find yourself halfway between Galway and Dublin on your journey, stop in for a pint of Guinness or a taste of Sean’s own crafted whiskey, and tap your toe to some Irish music. Sláinte!
Many thanks to Jennifer Kling for contributing to this newsletter.
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