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kernowclimber
2010-05-06 18:38:38
"Crinoid fossils in Dartry limestone" from kernowclimber Contract pics
Picture: Crinoid fossils in Dartry limestone (Contract 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.


RECENT CONTRIBUTIONS 1 2 3 .. 18 Next page >>
Track
Look out for easy path to summit from forest track.
Bunsen7 an hour ago.
Largely replicating track 1291, but showing the trail now going eastwward from the summit to T23444 94039.Views were ... walk, Len: 6.4km, Climb: 304m, Area: Carrick Mountain, Dublin/Wicklow (Ireland

  
Summit Comment
Carrick Mountain: If I got there quicker than you it's because I was...
Bunsen7 2 hours ago.
Visited on a beautiful, mild sunny day in Dec 2017. Parked at the forest entrance at Ballylusk as suggested by Track 1291, which I followed. Also had the benefit of the East-West Mapping East Wick...

  
Summit Comment
Ben of Howth: Here's to Howth!
Bunsen7 a day ago.
Having made my first proper visit there this afternoon and doing the Purple "Bog of Frogs" waymarked route (anti-clockwise with the detour to the Ben early in the walk), I found myself marvelling ...

Track
'Off-Grid' in Arctic Sweden: Trekking the Dag Hammarskjöldleden
mcrtchly a day ago.
We first visited Arctic Sweden in September 2016 and walked the middle section of the Kungsleden trail (MV track 3332). walk, Len: 110.7km, Climb: 1726m, Area: Sweden, Norrbotten ()

  
Summit Comment
Spinans Hill SE Top: Brissels or Brussels
Bunsen7 2 days ago.
Climbed both hills on 16/12/17, following the main route described by others here on MV.The forestry between the tops has thinned out a little (or so it seems by reference to previous comments) an...

  
Track
Glen o' the Downs Wood
jgfitz a day ago.
This woodland track can be accessed directly from N11 heading South. After Exit 9, there is a road sign for Glen o' the walk, Len: 5.9km, Climb: 183m, Area: Dublin/Wicklow (Ireland)

Summit Comment
Cloghnagaune: There must be an easier way!
Bunsen7 2 days ago.
This is a rather painful hill to summit from the obvious parking spot at the forest entrance to the south east. Following where others have gone I found myself wading through head high gorse to at...

  
Track
Cloghnagaune Summit and Stone Circle
Bunsen7 2 days ago.
This is a rather painful hill to summit from the obvious parking spot at the forest entrance to the south east. Follow... walk, Len: 4.0km, Climb: 144m, Area: Cloghnagaune, Dublin/Wicklow (Ireland) C

  
User profile
IainMiller
IainMiller 3 days ago.
A rock climber, hillwalker and guidebook author living, working and playing on the sea cliffs, sea stacks, mountain ranges and uninhabited islands of County Donegal. http://uniqueascent.ie/sea_sta...

Summit Comment
Roaninish: Roan Inish
IainMiller 3 days ago.
Roan Inish (Roaninish) is a low lying storm lashed small archipelago comprising five main islands and a large collection of tidal skerries. The islands are reasonably remote being 4 KM from the ne...

  
Track
The Beara-Breifne Way Day7
mlmoroneybb a week ago.
On Sunday, we were not attacked by the MacCarthys of Drishane Castle but started our walk on the O?Keefe Booning Castl walk, Len: 27.7km, Climb: 362m, Area: Paps/Derrynasaggart (Ireland)

  
Summit Comment
Inishbarnog: Roan Inish
IainMiller 3 days ago.
Roan Inish (Roaninish) is a low lying storm lashed small archipelago comprising five main islands and a large collection of tidal skerries. The islands are reasonably remote being 4 KM from the ne...


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