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OIDHREACHT NA COIRIBE

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The River Corrib and Geology

One interesting fact about the River Corrib is that it is said to have dried up during the years 1178, 1190, 1647 and 1683. Wilde, in his book ‘Lough Corrib, its shores and islands’ refers to work done by a Mr. Kinahan of the Geological Survey who ‘supposed’ that water had found its way through subterranean passages which had previously become blocked with sand and suddenly cleared. He suggests that this occurred at one point at Castlegar from where the water travelled underground out to Lough Atalia.

Primary Source: G. H. Kinahan. On the Formation of the Rock Basin at Lough Corrib. November 1866. Geological Magazine.


Angling Charts - Digital imagery of Lough Corrib and its bedrock

In this most useful website on AnglingCharts.com, there is a section on the 3D imagery of Lough Corrib derived using sidescan sonar data of the lake surveyed in 2012 and 2013. The information yielded by the research is currently being analysed at Trinity College Dublin. It provides interesting information on glaciation and about for example areas like Snadaun’s Hole where the lake suddenly changes from limestone to granite.

Currently on the website, there are images for the following areas: Ashford Bay, Doon and Doon Narrows, Snadaun’s Hole, Bure Rock Hole, Drumsnauv and Lackavrea Holes, Inishmicatreer Holes, Sandy Island Hole and Inchagoill.  Go to ‘relevant links’ for a direct link to the sonar images and descriptions.

Leac Aimhréi

This is a mountain on the south shore of the stretch of lake between the Hill of Doon and the mouth of the  Bealnabreac river.

Again, Wilde, in his book describes Leac Aimhréi as an uneven flagstone rising ‘abruptly to a height of 1,307 feet from the south shore of the upper lake, apparently bare, and barren even of heather, forms a step in the ladder of elevations that lead by gradation to Shannanafeola...etc.’ According to G.H. Kinahan of the Geological Survey who provided much information to Wilde, Leac Aimhréi is ‘principally formed of quartzites or quartz rocks, which were originally aqueous sandstones, that by some metamorphic power have been changed, and deposited in lamina’. He continues with ‘..they have the appearance as if they would split into flags, which is not the case, as they break into irregular lumps. This appears to be the reason for the name of the hill’.

Source: G.H. Kinahan. Geological Survey. This information appeared in ‘Wilde’s Loch Coirib its shores and islands, with notices of Lock Measga’. 4th edition 1955.

A Quick Look at Lough Corrib’s Geology

Wilde provides a very good picture of Lough Corrib’s geology which is non-technical and interesting. Michael J. Hynes has provided a summary of Wilde’s account and may be accessed by going to the ‘Downloads’ section on this page.

For those who are interested in reading Wilde’s account, please go to ‘relevant links’ on this page for more.

Lough Corrib-Lough Mask Isthmus

This narrow neck of land that separates Lough Mask from Lough Corrib is a karst landscape. Underground waters, flowing from several points from Lough Mask’s southern shores have hollowed out caves, rifts and chambers and these waters re-emerge via springs at Cong (north end of Lough Corrib). Swallow holes feature strongly in this region and a diagramatic map of these and of the Cong Canal can be viewed by going to the Geological Survey of Ireland website (go to relevant links).


Connemara Marble

What is commonly called ‘Connemara Marble’ is actually a serpentine or green calcareous rock and was found in various places between Lissoughter and Clifden. (Source: Wilde’s Loch Coirib).


The Cong Canal

Construction of the Cong Canal commenced with the intention of (i) reducing high winter water levels in Lough Mask, (ii) for navigation purposes and (iii) as a famine relief project. The plan was subsequently described as a disaster as it was discovered that the canal could not hold water due to the karstic landscape of the underlying bedrock. It therefore became known as the dry canal. In a more recent article called ‘The Dry Canal’ written by Luke Varley (Cúnga, Christmas 1997) the author disputes the claims that in effect the engineers’ ineptitude caused the problems. He argues that there were other factors at play including the fact that railways were beginning to open up around the country, thereby reducing the necessity for the canal to serve the purpose of navigation. Other factors included the increase in labour costs and the reduction in labourers due to the deaths of many during the Great Famine. The canal, however, did serve one important purpose - it managed to reduce the winter level of the lake by 7 ft. (Varley, 1997). To read this article go to the ‘downloads’  section of this page. Also, for more information on Cong, please visit ‘Built Heritage>Towns and Villages>Cong’ from the navigation bar above.

NATURAL HERITAGE - Geology

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