The Grianán of Aileach

Mark Wilson December 20, 2012 3:46 pm

GriananOutsideDONEGAL, IRELAND — In the northeastern part of the county, about 7 km west of Derry in Northern Ireland, is Greenan Mountain. On its very top is a spectacular ringfort called The Grianán of Aileach (“the Solarium of Aileach”, shown above). From it are spectacular views of the countryside 360° around. It is a majestic and yet rather lonely place, maybe because my new friend Andy Quinn and I were the only ones there. It was probably built in some form around the beginning of the common era and no doubt occupied by many successive groups. There is a burial mound on the site (a tumulus) that may date back to 3000 BCE. The local story is that it was originally a place to honor the sun (which I would not have minded seeing today).

The fort’s most prominent days were when it was the royal citadel of the northern Ui Neill sept of Aileach from the 5th to the 12th century. The stone portion of the fort was destroyed in 1101 by Murtogh O’Brien, King of Munster. His soldiers were ordered to take the fort apart and scatter its stones widely. In 1870 it was substantially restored to its present state.

The Grianán of Aileach was an excellent location to visit and have a look at the countryside of eastern County Donegal. The rocks exposed here are among the oldest in Ireland (Late Proterozoic to Early Cambrian).

GriananInsideThe inside of the circular Grianán of Aileach. There are three interior platforms connected by narrow stairs. There is some dispute over whether this was the original architecture of the ringfort before its destruction in 1101.

GriananRocksThe stones are mostly without mortar. They appear to be some kind of quartz mica schist.

GriananPanorama585I tried a panorama of Lough Swilly to the west of the ringfort. It doesn’t convey the real sweeping vista in 585 pixels wide, but you get the idea of a cool view!

GriananHolyWellThis is a “holy well” to the southeast of the ringfort. It is said to have been visited by St. Patrick himself. Then again, everyone wants a connection to The Man!

An Irish myth says that The Grianán of Aileach was built by King Daghda of Tuatha de Danann, and that the grave of his son lies beneath the fortress forever guarding it. In any case, we were suitably respectful of this ancient site.

 

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The wild northwest of Ireland

Mark Wilson December 19, 2012 1:28 pm

DonegalBaySunset121912DONEGAL, IRELAND — Above is an image of Donegal Bay at sunset. It is striking with its still water, wheeling gulls and glacially-rounded rocky islands. I am in County Donegal for a couple of days simply to see the place and get some hints of what is said to be the most complex geology in Ireland. There is also some evidence that the Wilson part of my family comes from the northwest of Ireland, so I might be seeing a bit of ancestral homeland. I am staying in the town of Donegal in the south of the county and will be visiting sites in the north and west tomorrow. Today, after a very bumpy flight and landing (Donegal airport is known for its high winds), I am exploring the town and its surroundings.

DonegalArrival121912This is the little County Donegal airport in the north. It is in one of the most isolated spots in the county — no bus line goes to it and taxis have to be ordered in advance from nearby towns. There were seven people on the plane, including the crew.

AbbeyHotel121912The Abbey Hotel in downtown Donegal. My home for a couple of days.

DonegalAbbey121912The ruins of the Franciscan Abbey in Donegal along the southern shore of the bay. It was built in 1474. As with many such structures in Ireland, it has a long history of sieges and intrigue. This portion has been used as a graveyard for centuries.

DriftDonegal121912The geology just along the shores of Donegal Bay seems complicated enough. There are some rocky outcrops I could not reach, along with exposures of boulder-studded glacial drift such as here.

AbbeyGraveyard121912The stones used in the local walls and in the remaining Abbey structures are diverse. Most are dark gray metabasalts or amphibolites, as seen in this graveyard wall lit by the setting sun.

AbbeyStone121912One prominent stone in the Abbey walls appears to be a quartzite metaconglomerate. Both these rock types are derived from local pre-Paleozoic outcrops.

Aodh_Ruadh_Ó_Domhnaill_585Finally, here is a dramatically-lit statue of Aodh Ruadh Ó Domhnaill (1427-1505) at the head of Donegal Bay and mouth of the River Eske. He was the subject of one of my favorite book-movie combinations as a kid: The Fighting Prince of Donegal. I also think he looks a lot like me, wouldn’t you say?

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Three Amigos in Dublin

Mark Wilson December 18, 2012 6:04 pm

ThreeAmigos121812_585DUBLIN, IRELAND — I have paleontological legends on either side of me, and the best of friends. Paul Taylor is on the left. He and I met in 1985 when I visited The Natural History Museum in London while on my first research leave. My Oxford host, Stuart McKerrow, said I just had to meet a young paleontologist at the museum because we had so many common interests. Indeed. Paul and I have had many adventures since through our long friendship. Also while at Oxford, Jim Kennedy told me that if I was interested in hard-substrate fossils I should take the train to Aberystwyth, Wales, and see Tim Palmer (above on the right). I did and have enjoyed a long and deep friendship and collaboration with him ever since. I think the world of these gentlemen and am grateful for all that they’ve taught me and the many research opportunities I’ve had with them. We had a very special dinner of traditional Irish stews this evening in Ireland’s oldest pub, The Brazen Head (established in 1198 — and I didn’t reverse any digits).

The Annual Meeting of the Palaeontological Association has now ended. Tomorrow morning I leave Dublin for a brief visit to County Donegal in the far northwest of Ireland. I hope to make a blog post or two from there, but I’m not sure I’ll have an internet connection. If not, the next posts will come from home in about a week. Slán agaibh!

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Geological fieldwork on the streets of Dublin

Mark Wilson December 16, 2012 6:25 pm

DublinRainbow121612DUBLIN, IRELAND — What could be more Irish than a rainbow over Dublin? (I know better than to write of leprechauns and pots of gold.)  It certainly crowned the end of a delightful afternoon spent with my friend Tim Palmer looking at building stones.

I am in Dublin attending the annual meeting of the Palaeontological Association. After a long editorial meeting, Tim and I went to the center of the city to look for a particular kind of stone that may have been used in the Medieval portions of the two Dublin cathedrals: St. Patrick’s (National Cathedral of the Church of Ireland) and Christ Church (also for the Church of Ireland but claimed by Roman Catholics — it’s confusing, especially since they are only a short walk from each other). Tim was looking for a limestone called Dundry Stone, part of the Inferior Oolite (Middle Jurassic) in Great Britain. It is notable as a non-oolitic part of the Inferior Oolite, made mostly of tiny fragments of crinoids and calcite cement. Tim quickly found the stone in both cathedrals.

StPatricks121612This is St. Patrick’s Cathedral. Its exterior is mostly restored, but the interior still retains part of its Medieval core. It dates back to 1191.

StPatricksChapelDoorway121612We asked at the door to see the oldest part of St. Patrick’s, and were immediately directed to this small chapel. At the time the cathedral was filling with people for a choir concert, so we were surrounded with the sounds of bells and children practicing their pieces. This chapel was used as a storeroom as well as a tourist site, so there are some incongruities (such as the folding chairs!). Almost all the stone is either covered with cement or replacements except in a few places, like the frame of this small doorway. That white rock is Dundry stone.

ChristChurchCathedral121612This is Christ Church Cathedral, just down the road from St. Patrick’s. (A rivalry between the two dates back to the 12th Century. Two cathedrals in one city is very rare, apparently.) Christ Church is the older of the two cathedrals, dating back to about 1040 when a Viking king of Dublin started construction. It also has a mostly restored exterior, and it too has Dundry stone making up surviving doorways and lintels.

ChapterHouse121612This is an excavated “Chapter House” just outside Christ Cathedral on the grounds. Tim Palmer can be seen in the corner making notes. Apparently monks, priests and other church notables would meet in this building and sit on the stone benches just like Tim. The stones in this ruin include original materials (like the Dundry) and a variety of other lithologies.

I had a great time learning about stonework, Medieval building techniques, and the various structural properties of limestones, all thanks to Tim. Tomorrow I’ll be back in the more secular pews of the paleontological meeting. I’m happy to have had this spot of unexpected fieldwork!

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Wooster’s Fossil of the Week: A bivalve boring from the Upper Ordovician of southern Ohio

Mark Wilson December 16, 2012 1:35 am

This week’s fossil is from close to home. In fact, it sit in my office. The above is a trace fossil named Petroxestes pera. It was produced on a carbonate hardground by a mytilacean bivalve known as Modiolopsis (shown below). Apparently the clam rocked back and forth on this substrate to make a small trench to hold it in place for its filter-feeding. This particular specimen of Petroxestes was found in the Liberty Formation (Upper Ordovician) of Caesar Creek State Park in southern Ohio. This is a place many Wooster paleontology students know well from field trips.
The original Petroxestes was at first known only from the Cincinnatian Group, but now it is known from many other places and time intervals, even including the Cretaceous and Miocene. It is a good lesson about trace fossils. They are defined by their morphology, not what organisms made them. It turns out that this slot-shaped trace can be made by other animals besides Modiolopsis, which went extinct in the Permian.

References:

Jagt, J.W.M., Neumann, C. and Donovan, S.K. 2009. Petroxestes altera, a new bioerosional trace fossil from the upper Maastrichtian (Cretaceous) of northeast Belgium. Bulletin de l’Institut royal des Sciences naturelles de Belgique, Sciences de la Terre 79: 137-145.

Pickerill, R.K., Donovan, S.K. and Portell, R.W. 2001. The bioerosional ichnofossil Petroxestes pera Wilson and Palmer from the Middle Miocene of Carriacou, Lesser Antilles. Caribbean Journal of Science 37: 130-131.

Pojeta Jr., J. and Palmer, T.J. 1976. The origin of rock boring in mytilacean pelecypods. Alcheringa 1: 167-179.

Tapanila, L. and Copper, P. 2002. Endolithic trace fossils in Ordovician-Silurian corals and stromatoporoids, Anticosti Island, eastern Canada. Acta Geologica Hispanica 37: 15–20.

Wilson, M.A. and Palmer, T.J. 1988. Nomenclature of a bivalve boring from the Upper Ordovician of the midwestern United States. Journal of Paleontology 62: 306-308.

Wilson, M.A. and Palmer, T.J. 2006. Patterns and processes in the Ordovician Bioerosion Revolution. Ichnos 13: 109–112.

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Wooster Geologist in Ireland

Mark Wilson December 15, 2012 7:28 am

IrishFlag121512DUBLIN, IRELAND — In a very quick transition from grading final exams in Wooster yesterday morning, I find myself now in downtown Dublin. I flew in last night to attend the 56th Annual Meeting of the Paleontological Association. I’ve been a member of this wonderful organization since 1985 — in fact, I’m one of the North American Representatives — and I love my rare visits to the main meetings. They are held throughout Europe to recognize the international base of the Palaeontological Association, with an emphasis on its European core. I am here representing the Paleontological Society in my role as Secretary. I am looking forward to meetings with my paleontologist colleagues, and to learning more about our craft and passion.

DublinPostOffice121512Since my first meeting is tomorrow morning, I spent some time looking at some of the historical places in the Dublin City Centre. Most impressive to me is the evocative Post Office, site of the failed Easter Rising by Irish nationalists in 1916. Above is the post office today. Below is the burned-out shell after the 1916 battle with British troops. Bullet scars are still visible in the stonework.

Dublin_Post_Office_1916

FourCourts121512The Four Courts, Ireland’s main court complex. The original structure was built in the 18th Century. The River Liffey is in the foreground.

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Wooster’s Fossil of the Week: A horn coral from the Upper Ordovician of Indiana

Mark Wilson December 9, 2012 1:34 am

This week’s fossil is a very common one from the Whitewater Formation (Richmondian, Upper Ordovician) exposed near Richmond, Indiana. It was collected, along with hundreds of other specimens, during one of many Invertebrate Paleontology field trips to an outcrop along a highway. The fossil is Grewingkia canadensis (Billings, 1862), a species my students know well because many made acetate peels of cross-sections they cut through it.

Grewingkia canadensis belongs to the Order Rugosa, a group commonly called the “horn corals” because their solitary forms (as above) have a horn-like shape. Children often think they are dinosaur teeth! It is so common in Richmondian rocks that it is sometimes used to indicate current direction. Its robust skeleton provided attachment space to many encrusting organisms, and it often has multiple borings in its thick calcite theca.

We believe that the rugose corals lived much like corals today. They sat partially buried in the sediment with the wide end of the skeleton facing upwards. A polyp sat inside the cup-shaped opening, spreading its tentacles to catch small organisms swimming by.

Grewingkia canadensis has a complicated taxonomic history. It is likely also known as Streptelasma rusticum, Grewingkia rustica, Streptelasma vagans, Streptelasma insolitum, and Streptelasma dispandum. G. canadensis is characterized by cardinal and counter septa (the vertical partitions inside the coral skeleton) that are longer than the other major septa throughout ontogeny (growth).
The handsome man shown above is, of course, a paleontologist. This is Elkanah Billings (1820-1876), Canada’s first government paleontologist and the one who named Grewingkia canadensis. (He originally placed it in the genus Zaphrentis.) Billings was born on a farm near Ottawa. He went to law school and became a lawyer in 1845. But he loved fossils and in 1852 founded a journal called the Canadian Naturalist (and Geologist). In 1856, Billings left the law and joined the Geological Survey of Canada as its first paleontologist. He named over a thousand new species in his career, and is best known for describing the first fossil from the Ediacaran biota — a critical time in life’s early history. The Billings Medal is given annually by the Geological Association of Canada to the most outstanding of its paleontologists.

References:

Billings, E. 1862. New species of fossils from different parts of the Lower, Middle, and Upper Silurian rocks of Canada. Paleozoic Fossils, Volume 1, Canadian Geological Survey, p. 96-168.

Elias, R.J. and Lee, D.J. 1993. Microborings and growth in Late Ordovician halysitids and other corals. Journal of Paleontology 67: 922-934.

Elias, R.J., McAuley, R.J. and Mattison, B.W. 1987. Directional orientations of solitary rugose corals. Canadian Journal of Earth Sciences 24: 806-812.

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Familiar Faces at AGU 2012

mpollock December 3, 2012 7:57 pm

San Francisco, CA – The annual meeting of the American Geophysical Union is the largest earth science conference in the world.

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With more than 20,000 attendees and about 3000 posters per day, you’re bound to bump into someone you know. Today, I ran into Wooster alum Jesse Davenport (’11). You may remember his senior I.S. adventures in Montana, working on 2 billion year old sheared igneous and metamorphic rocks. Jesse is currently a graduate student at Notre Dame and has shifted his focus to more recent (~80 million years old) basalts – a topic that I can finally relate to!

20121203-154459.jpg
Jesse is studying the compositions and textures of plagioclase and olivine crystals in basalts from the Detroit Seamount to better understand magmatic processes at ocean islands. (See a more complete explanation in his AGU abstract). It’s always fun to catch up with alumni who travel diverse paths yet have the common Wooster experience. If we’re lucky, Jesse will come to Wooster to share his research and experiences with GeoClub sometime this spring.

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Wooster’s Fossils of the Week: Shark teeth! (Upper Cretaceous of Israel)

Mark Wilson December 2, 2012 1:37 am

This week’s set of exquisite fossils is presented in honor of Andrew Retzler (’11) who has just had his Senior Independent Study thesis at Wooster published in the journal Cretaceous Research: “Chondrichthyans from the Menuha Formation (Late Cretaceous: Santonian–Early Campanian) of the Makhtesh Ramon region, southern Israel“. The above beauties are a mix of Scapanorhynchus teeth found in the southwestern portion of Makhtesh Ramon during Andrew’s study in the summer of 2010. We were ably assisted by Micah Risacher and Yoav Avni with these collections.

Andrew identified at least eight shark species and two other fish species in the Menuha Formation around Makhtesh Ramon. Most of the teeth are from a soft yellowish chalk with relatively few other fossils (mostly oysters, echinoids, foraminiferans and traces). They show that the Menuha was deposited in a shallow, open-shelf environment on the flanks of the developing Ramon anticline. So, they not only provide new information about Cretaceous sharks in the Middle East, they help sort out a complex stratigraphic-structural problem.

Well done, Andrew! (Andrew is currently a graduate student at Idaho State University. He is working on the Late Devonian Alamo Impact Event in Nevada with Dr. Leif Tapanila.)

Tooth of the shark Cretalamna appendiculata. Composite photo by Andrew Retzler.

Scapanorhynchus rapax, another shark species. Composite photo by Andrew Retzler.

An elegant Scapanorhynchus texana tooth.

Looking south at one of the productive exposures of the Menuha Formation (shown as the red dot) at Makhtesh Ramon. This is one of those amazing Google Earth images.

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Geology Heads to Melrose Elementary

sjudge November 29, 2012 5:24 pm

WOOSTER, OHIO — A “Volcano Team” headed to Melrose Elementary this week for an afternoon of fun with Marge Forbush’s 4th grade class. It was our annual fall trip to her classroom, and our task was to discuss the various geologic processes associated with volcanoes. The 4th grade students had already studied plate tectonics and volcanoes, so they were experts on the volcabulary, such as “Ring of Fire”, “magma chamber”, and “Pompeii”. Before Thanksgiving, they had even built active volcanoes in the classroom.

Our goal was to bring pounds and pounds of volcanic rock to show the students, so that they could see basalt, volcanic bombs, obsidian, pumice, tuff, and several intrusive rocks (granite and gabbro). Wooster students in the department each were in charge of specific stations around the classroom, and the 4th graders migrated between stations. Here’s a look at some of our Wooster students hard at work:

Lauren Vargo (’13) is a Wooster veteran of community outreach, having gone with both Greg Wiles and myself to several elementary schools in Wooster (Cornerstone, Melrose, and formerly Wayne).  She was in charge of discussing the impact of contact metamorphism with the students, and she had numerous metamorphic rocks on hand.

Matt Peppers (’13) seemed to field some of the most unusual questions of the day.  Here he is showing the 4th graders several different types of intrusive igneous rocks, along with the minerals in each rock.  Some of the students in Matt’s group are destined to become geologists, because they already could identify the minerals from their own “rock collections” at home.

Adam Silverstein (’16) was in charge of one of the more fun stations:  volcanic bombs!!  He used some of his knowledge from Meagen Pollock’s Natural Hazards course in order to talk to the students about hazards during a volcanic eruption.  As you can imagine, everyone liked to pick up the volcanic bombs, some of which were collected in the Black Rock Desert, Utah.

Another member of Wooster’s Natural Hazards course, Kaitlin Starr (’16), was a welcomed volunteer and an old friend.  Kaitlin, who was in charge of the lava flow station, is a Wooster native.  Kaitlin was actually a student of Marge Forbush when she was in the 4th grade, and so she received a round of applause from the students for coming back and visiting her old classroom.

We’ll be back to visit Marge’s classroom again in the spring, but next time our focus will be on fossils.  Stay tuned!!

 

 

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