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Western Marlbank; Tullynakeeragh Gravel LakeFermanagh
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Summary Full report
Site Type: Doline, Sinkhole
Site Status: PASSI
District: Fermanagh District Council
Grid Reference: H09763188
Rock Age: Quaternary (Holocene)
Rock Type: Limestone
Other interest: No data, No Data, doline, sinkhole

Summary of site:

This is a unique feature of the area. A stream sinks into the flat bed of a circular depression about 10m in diameter and fringed by Glenade Sandstone. The bed is formed of small tabular pieces of siltstone and shale from formations further up the mountain (see Cuilcagh Mountain, Key Site 20) and is normally dry, only forming a pond in wet conditions.

It is presumed that the stream enters the Dartry Limestone below the bed of this ‘lake’ which suggests that the Meenymore Formation between the Glenade Sandstone and the Dartry Limestone is either very thin at this point or breached in some way. The water entering the ‘lake’ has been shown by dye testing to enter Mistake Passage in Shannon Cave. This means that the stream is one of the true sources of the River Shannon.

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