Square at its base, measuring about two and a half metres on each side, and pierced by four furnace inlets, it is the most visible survivor of what was once a working iron industry in this part of Connacht. The remains of a house sit about forty metres to the east, a quiet companion to the chimney's more emphatic presence.

Lough Allen sits over one of Ireland's most significant iron ore and coal deposits, and the area around it saw serious industrial activity during the nineteenth century. The four furnace inlets in the Gubb chimney suggest a facility built for sustained, high-temperature work, most likely smelting or processing iron using the local fuel and ore resources that made this corner of Leitrim briefly competitive with larger industrial centres elsewhere. Spencer Harbour, on the western shore of the lough, would have offered practical access for moving raw materials and finished goods by water. The associated house nearby points to a site that was staffed and inhabited, not merely a seasonal or temporary operation, though the precise history of who ran it and when it fell out of use is not recorded here.