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Irish legends ignore the geological facts about the Giant’s Causeway

Posted in Geography, Geology, Legend, Myth on Thursday, 28 June 2012

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This edited article about the Giant’s Causeway originally appeared in Look and Learn issue number 743 published on 10 April 1976.

Giant's Causeway, picture, image, illustration

The Honeycombs, the Giant’s Causeway

The coasts of Ireland offer many scenes of beauty and interest. None is stranger than the Giant’s Causeway, the remarkable rock formation near Benbane Head, on the north coast.

The old Irish story which tells how it got this name is told in several forms, but in all of them the chief figure is the great hero Finn MacCoul.

The simplest version of the legend tells how MacCoul had been defied by a certain Scottish giant. In order to meet his rival, MacCoul proceeded to build a causeway all the way over the sea to the Hebrides. Eventually, the Scottish giant came striding across the causeway to put the Irishman in his place – only to find MacCoul more than a match for him, and to suffer utter defeat.

In reality, forces far more powerful than any legendary hero built this natural masterpiece on the Antrim shore. Fifty million years or more ago, immense subterranean pressures and disturbances forced rivers of molten lava to the surface. Flowing out through fissures in the earth’s crust, the larva cooled to form a layer of dark, close-grained rock.

The process went on for a considerable time. There were evidently two periods of eruption, with a long interval between. Evidence of this is seen in a stratum of a different rock which formed between the volcanic layers.

The great plateau of basalt, as this type of volcanic rock is called, now tilts downwards towards the west and south. It has long been overlaid by other rocks and soil, but in places, especially towards the north-west, outcrops of it appear. The spectacular display of the Giant’s Causeway represents the broken northern edge of the basalt plateau.

The rock shapes that make the causeway and neighbouring formations so fascinating are not normally found inland. They occur along the coast for the simple reason that they were caused by contact with the sea. The lava would naturally tend to set in solid masses. But when rapidly cooled by the water, it shrank and cracked – though in definite patterns. The result was formations of columns of rock such as those in the Giant’s Causeway.

Most of the columns are hexagonal (six-sided). There are exceptions – some of the columns have more or less than six sides. At least two have as many as eight. The latter are called the Keystone and the Wishing Chair.

Another interesting feature of the columns is the manner in which they are divided into sections by horizontal cracks. The neat joins look like the work of some master-craftsman.

The diameter of the basalt columns is 15 to 20 inches (38 to 50cm). There are estimated to be 40,000 of them, varying greatly in height, the tallest being over 50 feet (15m) high.

There are three main formations which make up the causeway. On the left, as one looks seaward, is the Little Causeway; in the centre is the Middle Causeway or “Honeycomb”, and extending some 700 feet (213m) out to sea on the right is the Grand Causeway. It is easy to imagine this as the remnant of a roadway that once spanned the sea.

Many single columns, or groups of them, have been given fanciful names because of their resemblance to familiar objects. Apart from the two already mentioned, there is the Fan, the Pot Lid and the Organ – a formation of pipe-like columns on the cliff-face. There is also a Giant’s Coffin, and a Giant’s Loom.

Every Ulster guide-book gives prominent place to the Giant’s Causeway. Nearly a century and a half ago, it was already attracting tourists – including visitors from the continent, who came in considerable numbers to see the Chaussee des Geants, as the French called it.

It looks most impressive when viewed from the cliffs on a rough day, with the surf breaking. The geological explanation of how the Giant’s Causeway came to be formed is perhaps less romantic than the version of the old Irish story-tellers. In one respect, at least, the legend of Finn MacCoul and his gigantic foe does have some connection with geological fact. On the Isle of Staffa, said to have been the Scottish giant’s home, there are basalt rock columns of just the same kind as those at the Giant’s Causeway. The most famous display at Staffa is in what is called Fingal’s Cave – and “Fingal” is simply a shortened form of Finn Coul, or MacCoul.

It is clear that the volcanic upheavals that created Ireland’s geological showpiece were not confined to the Irish side of the sea.

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