From Tulsk follow R367 southwest 3.3 km, turn left on Lismurtagh Road, after 1.1 km right after the forest on the right side across the field.
|karst lake Turlough
Matthew Parkes, Robert Meehan, Sophie Préteseille (2012):
The Geological Heritage of Roscommon. An audit of County Geological Sites in Roscommon.
Geological Survey of Ireland. Unpublished Report.
|As far as we know this information was accurate when it was published (see years in brackets), but may have changed since then.
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Brierfield Turlough forms a noticeable basin, bordered by a rock outcrop to the northeast and southwest. On the other sides it is bordered by sloping fields underlain by till. The depression is mostly a result of the last glaciation. It is shaped like a huge 8, an irregular lake in the northwest with a diameter of about 500 m, and another one in the southeast with almost a kilometer in diameter. This part is often still waterfilled, when the other one is already dry, and it borders the L1623 to the southeast. They are connected by a rather narrow channel, 700 m long and only 50 m wide. Another extension from the northwestern part to the west is rather narrow, almost 1 km long and up to 120 m wide.
The western arm is peaty and appears flat or slightly domed. The rest of the turlough is uneven and has shallow channels leading to the swallow holes. The basin is refilled by a semi-permanent stream from the northwest, and a spring at the southwest. From the peaty area in the east water seeps into the lake.
Like all turloughs in Ireland this seasonal lake is waterfilled during winter, and dries up during summer. The depression is a result of the glaciers of the last Ice Age, while the karstification started in the Tertiary. The swallow hole at the centre of the turlough is well developed and worth a visit while the lake is dry. It is best reached from the Lismurtagh Road in the north, at the edge of the forest, its a 400 m walk south.