Geological fieldwork on the streets of Dublin

December 16th, 2012

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!

Wooster Geologist in Ireland

December 15th, 2012

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.

The last holdouts of pagan Europe

July 14th, 2012

KÄINA, ESTONIA–The little island of Muhu between Saaremaa and the Estonian mainland, had a large prehistoric population — much larger than it has today. The Muhu Estonians built a large fort of stone heaps near the western coast opposite Saaremaa so that they could control the traffic and trade through the Small Strait. The remains of that fortification are seen above. In January 1227, Teutonic Crusaders cornered the last of the pagan Estonians in this stronghold. (They were, in fact, among the last pagans in all of Europe.) Reports say that 20,000 soldiers besieged 2500 Estonian warriors for six days here. All the Estonians were killed save one, who escaped by pretending to be a victorious crusader. Most of the stones of the fort were removed to build the causeway between Muhu and Saaremaa, but the site remains as a ring of earthen walls and a stone monument (below) marking the bloody battlefield.

Exploring the Estonian island of Hiiumaa

July 12th, 2012

KÄINA, ESTONIA–The Wooster/OSU geology team took a break today from our usual field routine. We spent the morning consolidating notes and specimens (yes, that means the students slept very late) and then the afternoon seeing some of the major Hiiumaa sites. The highlight was visiting Hiiumaa’s iconic attraction, the Kõpu Lighthouse on the Ristna Cape. It is the oldest lighthouse in the Baltic states and reported to be the third oldest continuously-operated lighthouse in the world. It was completed in 1531 and has been working ever since. The Hanseatic League demanded a lighthouse here beside the most important trade route in the Baltic Sea. The original light was a fire that required 1000 cords of firewood every year, nearly deforesting the surrounding peninsula. The Germans bombed it in 1941, but only damaged its optical structures on top. It was an important navigational aid until 1997 when it was replaced by a modern radar system.

A model of the medieval version of the Kõpu lighthouse in the Tallinn Maritime Museum. Access to the top platform was by a long ladder. The light was a bonfire of pine wood.

The lighthouse staircase is incredibly narrow and steep, being cut into the structure in the 19th century. (Prior to this there was a wooden staircase on the outside.) Richa is better built for such a place than me!

Richa and Jonah wanted an answer to the famous “O-H-I-O” pantomime our OSU friends like to construct, so they made a C-O-W version. The lighthouse window here at the top is the “O”, you see. Maybe it will catch on. Maybe …

Near the end of the afternoon we visited the Ristna Lighhouse and one of the westernmost points on the island. (This is where Alyssa found her famous trilobite.) Richa and Jonah noted that large igneous boulders make excellent posing platforms at the edge of the sea.

As a brief nature vignette, here is a dung beetle (Geotrupes stercorosus) we saw deep in the Estonian woods at our lunch spot. I’m sparing you the dung itself!

Wooster Geologist at Fort Ligonier, Pennsylvania: Choosing your ground geologically

June 5th, 2012

Fort Ligonier was built by the British in 1758 during the French and Indian War (or Seven Years’ War) along the Loyalhanna River in what is now Westmoreland County of southwestern Pennsylvania. It is a spectacular site today with a fully reconstructed fortification and an excellent museum. It gives us a chance to see how a military engineer used the local geology to build a successful fort in a difficult terrain.
The purpose of Fort Ligonier was to serve as the forward base for the capture of the French Fort Duquesne at the forks of the Ohio River. This was the most strategic site on the western frontier. The French and their Indian allies desperately wanted to preempt this attack by destroying the advancing British columns in the woods before they could assemble. The British and American colonists needed a robust road through the wilderness approaching Fort Duquesne, along with defensible strongholds. Fort Ligonier was the most critical of these positions, then, for both sides.
You would expect a fort to be built on the highest ground, yet Fort Ligonier is in a valley surrounded by commanding heights. The British knew, though, that the French and Indians did not have significant artillery in this theater. They could give up the heights so that they could use the Loyalhanna River as a defensible barrier against the inevitable infantry attacks. The site of Fort Ligonier also has small ravines on its other sides, forming a kind of moat. Most importantly, sandstone cliffs on the river side provide an unbreachable wall and an overview of the most likely approaches to the fort by the enemy. The British placed their largest cannon at the top of this cliff, surrounding them with an elaborate wooden stockade and sharpened obstacles.
The exposed rock of the Fort Ligonier cliffs is the Casselman Formation, a Late Carboniferous (about 300 million years old) mixture of shale, siltstone, sandstone and occasional coal beds. The particular unit here is a fine micaceous sandstone with cross-bedding. It was formed in an ancient river system. The cross-bedding and abundance of mica is a clue to this environment: the cross-bedding shows high-energy seasonal flooding; the mica flakes (the white grains seen below) show ebbs in water energy to near zero.
The French and Indians attacked Fort Ligonier on October 12, 1758, and very nearly took it. The British artillery sited on the sandstone cliffs was the deciding factor, though, and the besiegers retreated. Fort Ligonier swelled in population as British troops assembled for the attack on Fort Duquesne. In fact, in November 1758 it was the second largest city in Pennsylvania! (Among the British forces was the young George Washington.) The French saw the score and retreated from Fort Duquesne. The British captured this most strategic location and renamed the site “Pittsburgh”. Building and defending Fort Ligonier was key to this victory. By March 1766 the fort had served its purpose and was decommissioned.

References:

Fowler, W.M., Jr. 2005. Empires at War: The French and Indian War and the Struggle for North America, 1754–1763. Walker & Company, 360 pages.

Sipe, H.C. 1971. Fort Ligonier and Its Times. Ayer Company Publishers, 699 pages.

Stotz, C.M. 2005. Outposts of the War for Empire: The French and English in Western Pennsylvania: Their Armies, Their Forts, Their People, 1749-1764. University of Pittsburgh Press, 260 pages.

Nabataean water management in the northern Negev (circa 2nd Century BCE)

March 18th, 2012

MITZPE RAMON, ISRAEL–We had an earlier post about water management techniques by Iron Age peoples in the northern Negev. Today during our last period of fieldwork on this trip we ran into a complex Nabataean system in a valley a few kilometers north of Mitzpe Ramon. Nabataeans were an Arab people based in Jordan who spread in influence and settlement through this region from roughly the third century BCE to the third century CE. They are most remembered here for their water systems to support their small villages. The infrastructure they built is still used in many places by the Bedouin.

Today while exploring more Upper Cretaceous sites, we came across the cistern pictured at the top of this entry. It is a Nabataean structure because it is cut into solid rock (the Iron Age equivalents were mostly in clays) and it had a roof held up by the central pillar and interior walls. There are also steps cut into the rock for climbing in and out. The Nabataeans inherited the earlier Iron Age technology and improved on it by better water retention in the container, and reduced evaporative loss.

The cistern we just saw is pictured here from a distance. It is indicated by the tailings of rock debris produced in its construction. On the left hand side you can see a diagonal line of rock indicating part of the water catchment system. There is a similar line on the right, but it is very hard to see.

This even more distant image shows the cistern again as a cone of tailings in the upper left. The valley below is where the irrigated fields were. They are a bit complicated by a series of trenches dug across them recently. (This is an Israeli Army training ground.)

The low rock wall here held in soil for an irrigated field on the left side. The soil has been modified by the original farmers, who built it up with water-holding loess deposits. Some of these fields are still in occasional use by Bedouin who plant wheat in the ancient ground.

Iron Age water management in the northern Negev

March 16th, 2012

MITZPE RAMON, ISRAEL–This region has a very deep human history, and some of it is evident in subtle changes to the landscape itself. Throughout the northern Negev are simple stone structures that are sometimes called “Davidic forts” after King David of Israel. They are, though, a lot more mysterious and difficult to date. They are usually associated with cisterns and water systems, and so they may have indeed been guardposts of some kind. Who exactly made these buildings and the water infrastructure is unclear. All we can say is that they are Iron Age and show an early agricultural people who had skills in collecting and managing the scarce water resources of this area. We saw evidence of them today in the field north of Mitzpe Ramon. Above you see Yoav and Melissa walking by one of these open cisterns cut into Upper Cretaceous limestone (the Vroman Bank of the Ora Formation) and then dug below in shale and claystone.

The hillsides to the sides and above these cisterns have long ditches lined with slabs of limestone on their downward sides. These were designed to catch runoff water from the slopes above and direct it to the open cistern below. Some of these ditch-and-rock channels stretch for kilometers.

Here a ditch heads to a large cistern, recognizable immediately by the sediment tailings dug out of the hole. This system takes advantage of the heavy and infrequent rains in the northern Negev. Sheetflow and water in small natural channels is captured and sent along the gentle gradient to the cistern below. By keeping the water from flowing too fast these early engineers minimized erosion of their channels.

This is the second cistern we saw today. It is many meters deep and could have held a great deal of water year-round. Bedouin herders today still use some of these cisterns for their flocks.

The later Nabateans elaborated upon these innovations and made roofed cisterns to reduce evaporation (which is 2.5 meters of water per year in Mitzpe Ramon). Sometimes they dug their cisterns into solid limestone rather than shale so they could have a small top opening and large covered container below.

As I write this the wind howls and rare rain is falling on the Negev. These rock systems are still channeling water after 3000 years!

Wooster Geologists in the Wilderness of Zin

March 14th, 2012

MITZPE RAMON–Three times we cross Nahal Zin (or Wadi Zin) on our way to Makhtesh Gadol from Mitzpe Ramon. Nahal Zin is an intermittent stream, meaning it is dry most of the time, but during the rainy season can have a considerable flow, even to the point of flooding. I’ve always seen it bone dry. Nahal Zin is 120 kilometers long with impressive canyons in its upper region and meandering channels in its lower parts. It is the largest wadi that begins in the Negev.
The significance of Nahal Zin is that it is the defining feature of the “Wilderness of Zin” from biblical times. There is still some dispute about its location among biblical enthusiasts, but experts agree that it is essentially the northern portion of the Negev. The passions among the amateurs have much to do with the historicity of the Exodus events. This region was explored by T.E. Lawrence just before he became Lawrence of Arabia.
Google map image of Wadi Zin near Avdat. The red asterisks mark where it crosses Highway 40.

The Wilderness of Zin was on the southern border of Judah and is mentioned several times in the Hebrew Bible. Here are three:

“So they went up, and spied out the land from the wilderness of Zin to Rehob, to the entrance of Hamath.” (Numbers 13:21)

“The children of Israel, even the whole congregation, came into the wilderness of Zin in the first month: and the people abode in Kadesh; and Miriam died there, and was buried there.” (Numbers 20:1)

“The lot for the tribe of the children of Judah according to their families was to the border of Edom, even to the wilderness of Zin southward, at the uttermost part of the south.” (Joshua 15:1)

(Courtesy of Biblos.com)

During our work in the Negev we do not usually see much of biblical relevance, so living and working in the Wilderness of Zin reminds us of just how deep the human history here runs.

Wooster Geologist on the Crampton’s Gap Battlefield in northern Maryland

November 26th, 2011

In September 1862, Union forces under General George B. McClellan pursued General Robert E. Lee‘s Army of Northern Virginia through northwestern Maryland. Lee had invaded Maryland to demoralize the North ahead of the November elections, and to convince Europe that the Confederacy had legs and deserved recognition. A copy of Lee’s orders were lost (famously found by Union soldiers wrapping three cigars), alerting McClellan to his plans. The key to defeating Lee lay in capturing three passageways through South Mountain, one of which is known as Crampton’s Gap (shown above in this Google Earth image).
Crampton’s Gap as viewed from the southern side looking north. There were no structures here during the battle.

South Mountain is a north-south extension of the famous Blue Ridge into Maryland. It is a sharp ridge made of resistant metamorphic rocks, including gneisses, schists and quartzites. The slopes on either side are unusually steep and so passing from east to west over the mountain is best done through “gaps” made by eroding antecedent river systems. Water gaps are deepest and have streams currently flowing through them. (One is made by the Potomac River.) A wind gap was also made by river erosion, but the water was long ago snatched away by stream piracy. Crampton’s Gap (39° 24′ 36″ N, 77° 38′ 24″ W) is a wind gap less than 300 meters wide.

Quartzite exposed in Crampton’s Gap, probably from the Late Precambrian (?) Swift Run Formation Cambrian Antietam Formation (thanks, Callan).

On September 14, 1862, McClellan finally moved on Lee and attacked the three gaps through South Mountain to turn back Lee’s invasion. Crampton’s Gap was the southernmost part of what later became known as the Battle of South Mountain.
Union forces under Major General William B. Franklin, after a long preparation, attacked from the east a much smaller Confederate force at Crampton’s Gap. The Confederates resisted all day, taking advantage of the steep slopes and narrow pass with a battery of cannon. By the end of the day, though, the Union force broke through the Confederate lines, sending the remaining rebels down the western slopes. Strangely, Franklin failed to follow up on his victory, allowing the rebel troops to join Stonewall Jackson to capture the Union garrison and arsenal at Harpers Ferry. The overall battle was a Union victory as it blunted Lee’s invasion, forcing him to stand at Antietam and eventually retreat from Maryland. The resistant rocks of South Mountain protected his army long enough for him to frighten the Northern public, but those ancient wind gaps were his undoing.

How Fossils Saved Civilization: A National Fossil Day Talk

October 20th, 2011

WOOSTER, OHIO — National Fossil Day has now been in place for two years. Curiously enough, two Wooster alumnae, Erica Clites and Eva Lyon, have been critical organizers and promoters of this great event as Paleontology Interns with the National Park Service. It is sponsored by the NPS and the American Geosciences Institute (AGI). They even have an official National Fossil Day song! The College of Wooster is proud to be one of their academic partners on a list we hope will grow with the years.

As part of my contribution to National Fossil Day, I gave a talk to the Geology Club titled, “How Fossils Saved Civilization”. My title was inspired by “How the Irish Saved Civilization“, and like that book my tale had a bit of blarney in it. Nevertheless, I strongly believe that the proper understanding of fossils was one of the keys to the scientific revolutions of the 18th and 19th Centuries. Here’s to the beauty and wonder of fossils!

« Prev - Next »