In the vicinity of Lisacul, some 5km southwest of Ballaghaderreen, the River Lung takes a very devious route from northwest of Cloonacolly Lake (point A) towards Ballaghaderreen (point B). The direct route is impeded by a series of northwest - southeast orientated ridges of glacial till. Before the Lung River was deepened by arterial drainage, firstly in the 19th century and more recently in the 1980's, the low ground southeast of Lisacul was occupied by Figh Turlough. This drained through sinkholes during dry periods, and additionally by surface flow during the winter months.
1. GSI Borehole GSI-90-15
A borehole, drilled by the Geological Survey of Ireland in 1990, established the local geological succession, starting in the clean limestones of the Oakport Limestone formation, passing through the limestones and shales of the Kilbryan Limestone, the grey sandstones, silts and mudstones of the Boyle Sandstone, and terminating at a depth of 178m in the red sandstones of the Keadew Formation (Lower Devonian).
Artesian water was encountered in the Boyle Sandstone. The diagram below shows a possible explanation: an impermeable layer, possibly mudstones in the lower part of the Kilbryan Limestone, confines groundwater within the Boyle Sandstone aquifer. The water which feeds the aquifer enters on the hill slopes to the northwest. The height of the highest point of the confining layer determines a hydrostatic head. The borehole penetrated this confining layer, and the groundwater has (found its own level), which is above ground level at the borehole site.
A well-worn path from the bridge is evidence of continual use of this water supply, considerably better in taste than the public supply in the area- run the water for a short while before use to eliminate any iron taste that may have been acquired from the well casing etc.
The Lung River below Crunaun Bridge, from beside the borehole, showing the deepened cut which runs through the bottom-most beds of the Oakport Limestone Formation
2. Pollmore rising, grid reference 159625 290825
This is a substantial rising; dye tracing has shown that the water, in part, comes from locality 3. A visual estimate is that the outflow here was larger than in the inflow at (3), suggesting contribution from another source.
Pollmore, Creevy Townland
3. Unnamed sinkhole - Corracoggil North Townland
This is a typical sinkhole, muddy and dirty, used by cattle for drinking, and with an accumulation of timber and plastic where the water sinks. The stream sinks in thick-bedded clean (pure) Oakport limestone.
Dye tracing has revealed that water sinking here rises at both Pollmore (locality 2), and at Pollaneghbrick 4km away.
sink at grid reference 157995 289555
4. Pollawaddy Cave, grid reference 157280 289215
Pollawaddy is marked on the six-inch sheet Roscommon 13, and was noted some years ago by Donal Daly.
Most of this field party managed to fit into the first part of the cave. It was subsequently explored and mapped, and a description is to be found in a GSI newsletter article
5. Pollaghadoon - and the remains of Figh Turlough
Pollaghadoon, grid reference 160420 288915, with rath just beyond people
Figh Lake, or Turlough, was formerly much more extensive, but drainage works have reduced its extent. During the summer it drained through this sink, and two more to the west near Lisacul. In winter the lake filled up, overflowing northeastwards near Figh Bridge where there is now an arterial drainage channel.
We can see what the former high water level was by the fine platform rath beside the sink from which it derives its name.
On a personal level I note that a brother of my great8 grandfather, a Cormac MacDermot, is listed in the 1635-41 Survey and Distribution as owning some 427 "profitable" acres in this, and adjacent townlands.
The remains of Figh Turlough, in summer