Field trip report Bundoran ,Co Donegal. 10th -11th June, 2000

On the weekend of the 10th -11th June, 2000, the Branch set out to the northwest to explore the Carboniferous geology of the area around south Donegal, Sligo and Fermanagh. We were led by Dr Patrick McKeever from the Geological Survey of Northern Ireland. The trip proved to be one of the best yet, at least for those with a sedimentological bent! While the weather forecast was ominous we were lucky as it only rained during transit to the various outcrops.

The first area visited was sunny Bundoran to reconnoitre the Ballyshannon Limestone and the Bundoran Shale. Here we saw lots of fossils inclluding brachiopods and corals. We also saw the boundary between the shale and the limestone, the shale being deposited in a deep basin in front on an advancing delta. The Ballyshannon Limestone forms the base of the Viséan in the areas visited.

At Mullaghmore we examined the Mullaghmore Sandstone Formation which was deposited as a major delta from a landmass somewhere to the north. Here we saw two sequences one on top of the other. The shale/siltstone facies represents intertidal or lagoonal conditions, while the thick-bedded sandstone facies is thought to represent migrating river channel deposits. Some good examples of wave ripples were seen along with abundant evidence of burrowing and cross bedding.

At Streedagh Point we saw plenty of fossils including corals both colonial and solitary, these included Lithostrotion spp. and Caninia sp. Brachiopods were also seen in great profusion especially Productus sp. Someone even spotted what looked suspiciously like the pygidium of the small trilobite Phillipsia sp.

The sight awaiting us at Serpent Rock was even more spectacular fossil-wise. Here we say some very large Lithostrotion colonies, some well over a metre across and in life position. The solitary corals, all Caninia sp., were also large, some a metre long. The growth rings were clearly visible and are an indication of seasonal growth. Both of the above Formations are part of the Glencar Limestone. A short visit to Drumcliffe ,the burial place of the poet W.B.Yeats, saw us in more tourist mode.

Corals on the exposure at Serpent Rock

The last location on Saturday was Knocknarea, with some glacial and karst features including a turlough to be seen. The topography was explained in terms of the structural geology of the area. Some of the more adventurous then climbed to the summit.

On Sunday the first stop was Glenasheevar where we examined the exposure of the Meenymore Formation. The sandstone here was a very coarse one cemented with calcite and dolomite, which showed an orange colour due to weathering. Some thin mudstones were also present.

At Slisgarrow we were confronted with the Garrison Sill (dolerite). One particular individual was in his element here! Columnar jointing was clearly visible and metamorphosed limestone formed the floor of the quarry. The sill was of Palaeogene (Tertiary) age.

The next stop was Shannon Pot the starting point, if not the source, of the Shannon.

Next on the agenda was Killykeegan Nature Reserve. This could be described as a mini-Burren. Here we saw clints and grikes, a dry valley and swallow holes. The surrounding hills were pointed out as being ancient mudmounds. The limestone here is the Dartry Limestone.

John Deykin on Knocknarea with Sligo Bay and the Ox mountains in the background

The field trip ended with a visit to the Marble Arch Caves formed within the permeable Dartry Limestone. Three rivers enter the caves to emerge as the one river, the Cladagh At the base of the gorge one could clearly see where the water emerged on contact with the underlying shale. The cave trip started with a boat trip through the river system followed by a tour of the cave system with all its features.

All who attended the weekend (some twenty-one people) agreed that this was a very enjoyable field trip due in no small part to the leader Patrick McKeever. Many thanks to Patrick.

John Deykin