The structure is a sub-megalithic cist, a type of stone-lined grave box that falls between a simple slab-covered pit and the grander megalithic tradition; this particular example is modest even by those standards, its open chamber measuring just 1.2 metres long, 0.65 metres wide, and 0.55 metres high. A single sidestone runs along the north face, another along the south, with a backstone set into the eastern end and one roofstone laid across the top. It is oriented east to west, a common alignment in prehistoric burial practice, and sits in open pasture roughly 600 metres south-west of a larger multiple-cist cairn.

What gives this unassuming box of stones a second layer of meaning is a local tradition recorded by the antiquarian J. Grove White in the early twentieth century: the cist was used as a mass rock. Mass rocks are a recognisable feature of the Irish penal era, the period following the Williamite Wars when Catholic worship was driven outdoors and priests celebrated Mass at improvised outdoor altars, often flat-topped stones in remote locations. The idea that a community would press a prehistoric grave into service as a clandestine altar is not without parallel in Ireland, where landscape features of all kinds were adapted to urgent purpose. Here, a structure probably built for the dead was temporarily reassigned to the living, and to a form of religious observance that carried considerable personal risk for those attending.