Dear Old Hibernia

 A short while ago, I made the  trans-Atlantic flight to visit my girlfriend who was finishing her degree in the UK. As a break from the vivas and theses, we made a quick trip to the little exclave of Northern Ireland. The Emerald Isle is no less verdant and attractive on the Commonwealth side of the line, and the landscape abounds with geological curios. 


We followed the northern coast, where primeval-looking white washed cottages perch on the shoulders of big grassy hillsides. A short trip down this coastal highway will lead you to "The Giant's Causeway", a segment of coast honeycombed with columnar basalt that has become the most visited tourist site in Northern Ireland.

 

The rich-colored rocks form giant pillars in some places and have been worn down to a neat polygonal cobblestone pattern in others. The banner photo for this blog shows an example of the latter. This "columnar basalt" is the result of an ancient lava flow, where low-viscosity molten rock poured out into broad plains and plateaus. In the case of this site, the flood basalts stretched out for over 700,000 square miles during the Paleogene period  (50-60 mya.) As the lava quickly cooled, it contracted vertically, then horizontally, creating the regular network of fractures.

           (1768 engraving by Susanna Drury)

The Irish of years past must have agreed that the eroded pillars look like an oversized cobble-stone path. The etiological myth of the "Giant's Causeway" is built around the cultural hero Finn McCool (Fionn mac Cumhaill in the original Gaelic.) In legend, this giant hunter-warrior built the Giant's Causeway as a bridge to Scotland in order to keep his feet dry. In another version, he built the structure while preparing to attack a Scottish adversary, but then tore it up when he saw the size of his opponent. The geology behind this tall tale is not entirely baseless- the same basaltic plateau that we see in Ireland once stretched all the way across the Irish Sea and similar columnar basalts can be found at Fingal's Cave in Scotland.

The real "bridge to nowhere"

If Finn McCool's feet supposedly pounded natural wonders into the Emerald Isle, than his name lent symbolic power to its politics. The Fenian Brotherhood, formed by in 1858 by Irish emigrants to the US gave expression to anger and frustration at centuries of British colonial rule in their home country. Incensed by unfair land tenure and economic oppression, this  movement organized political support for Irish independence and even went so far as to invade forts in British-administered Canada. The idea of a few hundred 19th century Irish nationalists invading Canada seems quaint nowadays, but a quick trip to Belfast shows that the tensions are not that far behind us.

The industrial cities of Belfast and Derry are both littered with colorful murals, some pleading for peace- others with more sectarian aims.  

On the left is a mural in the bricked-in Catholic ghetto of Free Derry. The dove grows out of an oak leaf, a traditional symbol of the town. The frightening mural on the right stands on a Unionist stretch of the Shankill Road in Belfast. The caption reads "A Protestant wife defends the farm against intruders."The very day after our visit, a traditional celebration in a Unionist neighborhood went horribly wrong, with several police offers being injured by gunshots and rocks.

Imagine the earth six hundred million years ago. The Irish landmass was actually two separate islands, divided by the vast Iapetus Ocean. Northwestern Ireland balanced on a microplate grouped with Laurentia while southern Ireland (along with the mass of England) belonged to the smaller Avalonia continent.

Map courtesy of Wikiuser Woudloper. The red lines represent sutures and orogenies.

It took 50 million years, but tectonic engines brought these disparate parts crashing together in a fateful union. Ireland has been one island since. How much longer will it take for the residents to realize that today's partition is only in their minds?

Courtesy of NASA.