ESCR - Outlying sites in Fermanagh & Tyrone; Garrison

Earth Science Conservation Review

Summary Full report
Outlying sites in Fermanagh & Tyrone; Garrison	Fermanagh

Site number:	1163
ESCC:	IC
Locality Type:	Karst	Status:	ASSI
Grid Reference:	G970509,G968464,H047474 Centroid, Not Entered
Google maps:	54.40715,-8.04618
County:	Fermanagh	Council area:	Fermanagh & Omagh District Council
Period:	Quaternary, Carboniferous
Stages:	Asbian, Holocene, Visean
Lithostrat:	Dartry Limestone Formation, Glenade Sandstone Formation, Glencar Limestone Formation, Knockmore Limestone Member, Meenymore Formation, Quarry Sandstone Member

Site Description
Highlights:
Fresh water littoral karren at Lough Formal. Natural bridge on the County River and short active river cave on the Roogagh River at Tullybelcoo with large population of common cave spiders (Meta menardi).
Introduction:
The three sites described here are located within the Garrison area. History of Exploration: Lough Formal is mentioned in Jones (1974) and was visited by Leeds University Speleological Society in 1972. No sites of speleological interest were found. The other two sites are known locally but are not of great interest to cavers and there are no known published records. Minor Speleological Sites: Ground Bridge on the Roogagh River (G970 509), Natural bridge over the County River (G968 464). Surface Karst Features: Lough Formal (H047 474).
Description:
(i) Lough Formal Lough Formal is a small mountain lake situated at 240m amsl on a faulted outlier of the Knockmore Limestone Member in the Big Dog Forest. On the northern shore of the lake the Knockmore Limestone is exposed and a substantial notch has developed at water level. Two small hills, Formal More and Formal Beg, are also developed in the Knockmore Limestone and have small areas of exposed bedrock with some karren features. (ii) Ground Bridge on the Roogagh River The Ground Bridge on the Roogagh River at Tullybelcoo is a short active river cave. The passage is ~45m long and the Roogagh River flows through an outcrop of the Dartry Limestone. The sink is very close to the contact between the Dartry Limestone and the Quarry Sandstone Member. The Dartry Limestone dips southeast at 15° and is thinly bedded (~30-40cm) with the roof of the cave developed on the bedding. Entering the cave at the sink a sump is reached within 10m while the resurgence cave can be followed for a short distance over sandstone boulders until it gets too tight. (iii) Natural bridge over the County River This natural bridge is situated on the County River on the border between County Fermanagh and County Leitrim leaving only half the feature in Northern Ireland. It is adjacent to a scheduled archaeological site and the bridge must have been significant in the siting of the adjacent monastery. The bridge is developed in a small outcrop of the Knockmore Limestone, has a span of ~8m and is 4m in breadth. There are foot caves in both north and south banks and a short joint controlled rift at right angles to the river bank cuts the cliff lined bank next to the bridge.
Importance:
All three sites are examples of karst landforms which are not seen elsewhere in Northern Ireland. The spider population in the Ground Bridge is notably large and this species has been described as relatively rare in the caves of Fermanagh (Adair, 1974).
Interpretation:
Lough Formal: The water level notch has developed by corrasion and corrosion of the limestone by the lake water and the present roof level seems to indicate a previously higher lake water level some 50cm above the present level. Both the Natural bridge over the County River and the Ground Bridge on the Roogagh River are the result of rivers finding a course through bedding fractures in small limestone outcrops.
Conclusions:
CONCLUSION The Lough Formal site is of significant karst geomorphological and geological interest and quality in a Northern Irish context. The Ground Bridge on the Roogagh River is also of karst geomorphological and geological significance and has biospelological importance. This scientific interest justifies a refuse clean up programme which would reinstate the site's quality. The natural bridge on the County River is on the Border and the bat roosts are in the Republic. The Northern portion of the feature does not justify designation.
Notes:
For site specific information see; Key Site 428 - Roogagh River ground bridge Key Site 429 - County River natural bridge Key Site 430 - Lough Formal. For information and reference lists on the systems and features of other outlying karst areas in Fermanagh and Tyrone see; Key Site 1164 - Fardrum Key Site 1165 - Kiltierney Deer Park Key Site 1166 - Knockninny & Molly Mountain Key Site 1167 - Lough Lee-Binnawooda area Key Site 1168 - Slieve Beagh area. BIOLOGICAL INTEREST (i) Ground Bridge on the Roogagh River The downstream cave entrance supports the largest population of the common cave spider (Meta menardi) known by the authors. The resurgence has a net of webs which extend across the whole of this low wide entrance (12m wide by 1m high) and the population occupies the first 10m of the cave. Dippers (Cinclus cinclus) also nest at this entrance. (ii) Natural bridge over the County River A phreatic dome in the south bank foot cave appears to be an intermittent bat roost and fox (Vulpes vulpes) appear to occupy a short cave on north bank.

Keywords
Rocks:	Limestone
Structures:	bedding
Geomorph:	cave, clastic sediments, organic sediments, sump

Access
Planning:	HISTORY OF EXPLORATION Lough Formal is mentioned in Jones (1974) and was visited by Leeds University Speleological Society in 1972. No sites of speleological interest were found. The other two sites are known locally but are not of great interest to cavers and there are no known published records.
Management:
Lough Formal lies with Forestry Service land and Formal More and Formal Beg have not been planted. The site is in a good state of preservation. The Ground Bridge on the Roogagh River has suffered from rubbish dumping. It appears that the sewage outflow from a now uninhabited house was directed into the upstream cave entrance and that household rubbish was regularly dumped into the river. Both sources of pollution seem to have ceased.

References (28)
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Oswald, D.H., 1955. The Carboniferous Rocks between the Ox Mountains and Donegal Bay. Journal of the Geological Society of London, vol. 111, pp.167-186.
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Map(s):	Two areas have been outlined on OSNI 1:10,000 sheets 209 and 189; LF 1. Lough Formal. GB 1. Ground Bridge on the Roogagh River.
Record type:	ESCR report
Entered by:	E M Porter

Enlander, I., Dempster, M. & Doughty, P., 2026. Outlying sites in Fermanagh & Tyrone; Garrison, County Fermanagh, site details. [In] Earth Science Conservation Review.
https://www.habitas.org.uk/escr/site.php?item=1163. Accessed on 2026-11-08.