G.H. Kinahan, a 19th-century geologist and antiquarian, documented this monument in 1889, describing it as a double-chambered fosleac built from large, squarish stone blocks. The term 'fosleac' was Kinahan's own designation for structures constructed using flat stones or elongated blocks, though the exact nature and purpose of this particular monument remains uncertain.

What makes this site particularly mysterious is its complete disappearance. Despite Kinahan carefully marking its location on his field maps, now housed in the Geological Survey Office in Dublin, no trace of the structure survives today. The Ordnance Survey never recorded it on their detailed 6-inch maps, suggesting it may have already been in poor condition or partially destroyed by the late 1800s. Land reclamation work in the area likely sealed its fate, removing the last vestiges of this enigmatic monument.

Without the structure itself to examine, archaeologists can only speculate about its original function. The double-chambered design and construction method suggest it could have been a type of cist burial, a common form of prehistoric monument in Ireland. These stone-built burial chambers typically date from the Bronze Age, though without excavation or surviving remains, the true age and purpose of the Legmuckduff fosleac will remain one of Donegal's lost archaeological puzzles.