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Geology

In Cloneen and its environs, we are fortunate to be so close to the most famous mountain in Ireland, Slievenamon. Though it is not very high, 720 metres, it is gently sloped, thus easy to climb. Slievenamon has much history attached to it and has many stories and songs, which were inspired by its magical qualities. Many a battle was fought on or near its slopes. It has a range of geological formations, including limestone at its base, slate, sandstone conglomerate rock, scree and mudstone.

The Anner River valley, close to the foothills, has alluvial deposits of gravel and sand, some of which are used for building purposes. These deposits were laid down during the ice thaw.

Ten thousand years ago Slievenamon was completely covered by ice, and when the thaw set in, great ice sheets on the move dragged massive rock boulders down the slopes, and deposited them all over. Even after ten thousand years this can be verified by inspection of the boulders, as the grooves left by rocks sliding over other rocks leaves what is called striation marks. These can be viewed on many of the larger boulders scattered here and there in the valley and uplands. Glaciers and great rivers of melt-water laid gravel deposits, and set the scene for much of the landscape we have today. It is safe to say that the higher reaches of Slievenamon was much more rugged, with large outcrops of rock and at least one corrie lake, where the black bog now exists this area of the mountain is an important aquifer, it functions like a giant sponge holding millions of gallons of water.

Blanket Bog covered in heather

Blanket bog on Slievenamon covered with heather

Limestone is the underlying rock in the area. In places it is close to, and in some areas, above the surface. Cloneen, Mullinahone, and Killusty had well worked limestone quarries in years gone by, as can be seen from the structure of walls, houses, and local roads. Limestone is a soft rock. Constant weathering over millions of years created caverns and caves, as in the Bulls Hole at Mullinahone, at Mullenbawn and the Priesttown caves. Many holes, called slugrah, where water just disappears down into the ground and flows underground, sometimes for considerable distances, through openings in the rocks, emerges in a lovely clear well or stream. More water stays in caverns underground and has to be pumped to the surface (these are known as Artesian wells)

Water from a limestone aquifer can be a problem for domestic appliances, as limestone is partially soluble. Calcium carbonate within the rock dissolves in the water. This sticks to kettles and pipes etc and causes problems (though not to health). The old remedy to stop lime sticking to a kettle was to put a small round sandstone in the kettle and, when it began to boil, the stone would move around and collect much of the lime within the appliance.

South east of Cloneen, on the lower slopes of the mountain, what is likely to be a geological feature, called a moraine, can be seen. It is created by retreating glaciers which carried huge amounts of deposits within or in front of it. When the glacier runs out of pace, the debris which it carries is deposited and leaves behind a large mound which is tapered. These features can be seen all over the island of Ireland and are comprised of gravel and sand or till, and are of geomorphological interest. They are also of huge economical importance as these deposits are exploited for road making and house building.

On the eastern side of Slievenamon lies an area called the Slate Quarries. This is geologically different to most of the rest of the mountain. It was formed five hundred and forty million years ago by heat and pressure. This type of rock is called metamorphic {from the GSI survey}. Grey slates and hard greys were quarried here and many men were employed on the workings. The remains of their dwellings can still be seen, as can the tailings from the works, and also very deep, dangerous ponds.

Author: P. Clancy

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