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| Cahir Castle |
With the office based preparations for the Dublin Stone Show well under way, my thoughts turned again to the further exploration of rural Ireland. The summer months had flown by and, now that my friends at Dun an Óir had all gone home, I decided to escape from Dublin for a week and catch up with some field work.
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| A rainbow at Cahir Castle |
As
with the South Yorkshire RIGS, many of the Irish County Geological Sites include
redundant and active building stone quarries and so my trip had two purposes.
Firstly, I planned to survey several of these quarries and, secondly, I intended
to visit as many ancient monuments as I could and see how the materials used to
build these and other historic buildings related to the local geology.
Driving
across the Carboniferous limestone of the midlands of Ireland again,
there was no obvious interest for the geologist, until the Slieveardagh Hills came into view. Although rising only to 349 metres,
this outlier of coal bearing Carboniferous sandstone and shale takes you by surprise when it pokes
out of the surrounding landscape.
I didn’t stop or take a single photograph until I reached Co. Tipperary. The only reference to this county that I knew came from a song. At Cahir, with its castle - located on a small island in the River Suir - you can imagine why this place was chosen to build a stronghold, in 1142. With rocky outcrops of Carboniferous limestone, upon which to lay the foundations, and a fast flowing, swirling river on one side, it is easy to defend...
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| The gateway to Cahir Castle |
This
limestone is a hard, intractable material and the bulk of the masonry comprises
roughly squared and coursed rubble limestone walling and, just by the entrance,
a natural outcrop shows the irregular bedding structures that make the working
of this material so difficult.
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| An outcrop of Carboniferous limestone at Cahir Castle |
For
dressings, and sections of newer walls, Devonian Old Red Sandstone has
been brought in from further afield. This is not the best quality building
stone, but larger blocks can be extracted from the quarry and it can be
cut and shaped much more easily than the limestone and gives strength to points
of structural weakness in the building.
Although I didn’t search for fossils in the limestone, the beds are tilted and the contrast between the two stones – their colours, textures and chemical and physical composition - provides a simple lesson in Irish geology...
Although I didn’t search for fossils in the limestone, the beds are tilted and the contrast between the two stones – their colours, textures and chemical and physical composition - provides a simple lesson in Irish geology...
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| Old Red Sandstone |
