The souterrain, a type of man-made underground chamber or tunnel typically associated with early Irish settlement sites and used for storage or refuge, had gone entirely undetected until the machinery went through it. By the time anyone could properly document it, the structure itself had been destroyed.

What survived the quarrying was rather more remarkable than the passage itself. Standing free inside the chamber was a slab of shaly sandstone bearing an ogham inscription, the early Irish script in which letters are represented by groups of notches and scores cut along the edge of a stone. The slab measures just under one and a half metres in length, though its upper end had been broken off in antiquity, meaning the inscription was already incomplete long before 1953. The surviving text, cut in well-spaced, narrow scores along the dexter angle of the stone, reads: BRANADDOVMA MAQI QOLI MUCOI DOVIV, with the final character ambiguous, possibly ending in N or S. The formula is characteristic of early ogham inscriptions, with MAQI meaning "son of" and MUCOI indicating tribal or ancestral affiliation. The personal name Branaddovma and the lineage it records connect this stone to the broader world of early Irish genealogical commemoration, a world in which erecting a named stone was a way of asserting identity and territorial claim. The stone is now held in the County Museum in Tralee, catalogued as L224.