Great Orme revisited
At 10.45 am, Friday 20th September, members from both the Ruthin & Berwyn geology groups met in the car park on the summit of the Great Orme, Llandudno for our final field trip of the year. October's trip is a guided geological walk around Ruthin town and the following months until spring will be geological talks/presentations held in Ruthin library.
The weather was excellent, sunny, a very light breeze and clear views whichever way you looked. I'm sorry that so many members were unable to join us. Everyone received a handout covering the basics of what we would see and how it was formed. A short H&S talk, a check for sensible shoes and making sure we had enough hard hats to share for the first half of the trip. Everyone was warned about the dangers of standing beneath overhanging rock.
The Great Orme.
A syncline, limestone headland. Sequences of solid limestone, rubbly limestone and a thin layer of mudstone.
Bishop's Quarry.
A limestone quarry, Carboniferous rock formed 350-300 MY. A SSSI site. ( Sites of Special Scientific Interest) So no hammers allowed. Loggerheads Limestone beneath the Cefn Mawr formation. Layers of thin mud stone between the limestone layers were deposited when the sea levels fell and retreated during the many Ice Ages.
Fossils: (brachiopods, crinoids & corals.)
There is a quarried area of rocks just full of the above fossils. So it's quite an experience to see such a vast amount all crowded together.
Limestone Pavements & Sinkholes.
We spent half an hour for lunch, removed our hats then set off in the direction of where we thought the sinkhole was. These Loggerhead limestone pavements cover the largest area in Wales. During the last Ice Age 1 kilometer of ice lay above the limestone 60,000-12,000 years ago. This moving ice scoured the uppermost layer of limestone leaving it flat and devoid of any soil or other coverings. We saw and discussed the formation of Clints & Grykes in the pavements.
Group member Richard found the sinkhole, a round depression in the limestone with fluted edges. Luckily the centre part is filled in. Sinkholes in limestone occur when the roof of an underground cave collapses. Our December meeting is a presentation on sinkholes.
It was a lovely end to this year's field trip and the weather was great.
Isabel
Return to Geology group page.