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kernowclimber
2010-05-06 18:38:38
"Crinoid fossils in Dartry limestone" from kernowclimber Expand pics
Crinoid fossils in Dartry limestone (Expand pics)
Reading the rocks beneath our feet: crinoids
Simon has suggested that a description of a crinoid (mentioned in my recent Benbulben post) could be useful to other walkers who might encounter interesting fossils in the rocks while out and about in our mountains. I’m not a geologist, but mcrtchly is, so I thank him for aiding in this brief description.

Crinoids (also known as sea lilies) have been around for about 530 million years, first appearing in the fossil record of ocean sediments deposited during the Cambrian Period. These delicate creatures related to star fish, sea urchins and star dollars, resembled a flower complete with stalk and root-like parts and formed vast colonies on the floors of warm, shallow seas all over the globe during the Paleozoic Era. Some cast off their stalk and root-like anchor to become free-moving. However, many species of crinoids died out in the mass Permian extinctions, but the few that survived include the ancestors of the present day species which tend to inhabit deeper waters.

The bodies of crinoids are comprised of calcareous (calcium carbonate) plates. When these creatures die and sink to the sea floor, millions of their bodies compact over time to form thick limestone beds, some of which are eventually uplifted to form new land. As crinoid skeletons are made of calcium carbonate they fossilise easily. The stalks are the commonest parts to be fossilised and often look like stone worms when seen lengthwise and may protrude slightly from weathered rock.

Benbulben Mountain is comprised of rocks formed around 320 million years ago in the Carboniferous Period. The land that became Ireland then lay on the southern edge of a continent called Laurentia that straddled the Equator and was subject to repeated periods of inundation by the Tethys Sea. A hard and resistant rock named Dartry limestone forms the upper cliffs and precipices of Benbulben and lies atop softer shales overlying Glencar limestone.

Our fossil find (photographed) was made close to the top of the waterfall on the way up to the Benbulben plateau from Glendarragh Valley and shows fragments of crinoid stalks trapped in Dartry limestone. Benbulben is a good place to look for all sorts of fossils and near the bottom of the waterfall we found a fragment of a giant coral we believe to be Caninophyllum that thrived in the warm Equatorial waters off Laurentia.
Dessie, here's a c.. by paulocon   (Show all posts)
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RECENT CONTRIBUTIONS 1 2 3 .. 17 Next page >>
Track
Central Dingle Quartet from Anascaul
Bunsen7 20 hours ago.
Follow the track from Anascaul lake car park northwards up onto the mountain plateau.Track leads northwards from lake... walk, Len: 15.8km, Climb: 949m, Area: Stradbally Mountain, Central Dingle (Ire

  
Summit Summary
Seefin Mountain W Top: Bog and rough ground.
Collaborative entry Last edit by: melohara 2 days ago.
Car park space at R66276 16811. Over or around the gate and head uphill on a good track that crosses the hill near the summit of Seefin Mountain East top.Follow the track on downhill from the cres...

  
Track
Pic du Midi d'Ossau
David-Guenot a day ago.
The idea came from my 60-year-old, freshly retired neighbour, as we and some other members of the local badminton club m walk, Len: 16.2km, Climb: 1353m, Area: France, Nouvelle-Aquitaine ()

Summit Summary
Seefin Mountain E Top: Up the old bog road.
Collaborative entry Last edit by: melohara 2 days ago.
Car park space at R66276 16811. Over or around the gate and head uphill on a good track that crosses the hill near the summit.On the crest of the hill the summit cairn is over a wall to your right...

  
Summit Summary
Seefin South-East Top: Seefin South East Top is easily visited
Collaborative entry Last edit by: melohara 2 days ago.
Seefin South East Top is easily visited from the track leading to Seefin Mountain East Top and Seefin Mountain West Top which starts st R66276 16811. Just follow the track to R65202 17892 from whe...

  
Summit Comment
Carnaween: The visitors book box near the summit
Aidy 6 days ago.
Just wanted to show the brilliantly constructed little box which contains the visitors book. It was too wet and windy on my visit to take it out and risk ruining it. A few shafts of light breaking...

Summit Comment
Carnaween: Bad Weather Adding Drama To Great Views
Aidy 6 days ago.
I used the commonly taken route from Disert Graveyard (worth a visit in its own right) over ground that was alternatively boggy or pretty steep. It was freezing cold in these parts, with a strong ...

  
Track
Pic Rouge de Bassiès
David-Guenot 2 days ago.
This was the first of the two big hikes I did in the Pyrenees in summer 2016. Hiking in the summer often means a sunny d walk, Len: 16.3km, Climb: 1342m, Area: France, Midi-Pyr?n?es ()

  
Summit Comment
Corrin: A family stroll.
David-Guenot a week ago.
Climbed this hill in November 2014, with a friend who used to live in the area. Starting at the Coillte car park, we did a nice loop on the forest paths, circling around the hill in an anticlockwi...

Forum: General
MV Mountain Gathering 2017
Onzy 4 days ago.
Always a great night ... all welcome.

  
Summit Comment
Luggala: Fancy View from White Hill
davsheen 2 weeks ago.
Autumn's evening view across to Luggala/Fancy from White Hill on route down from Djouce using the Wicklow Way boardwalk section.

  
Summit Comment
Binn Charrach: The peat-hag capital of Connemara
markwallace 2 weeks ago.
The descent from Benbaun to the R344 via Knockpasheemore/Binn Charrach is hard going after a day in the Bens. The Knockpasheemore ridge looks nice and flat from below, but is boggy, undulating and...


RECENT CONTRIBUTIONS 1 2 3 .. 17 Next page >>