That uncertainty is itself part of what makes it worth knowing about. The stone in question was recorded as bearing cup marks, the shallow circular depressions commonly pecked into rock surfaces during the prehistoric period, though their precise age and purpose remain subjects of debate among archaeologists. What makes this particular example unusual is not so much what it showed as the doubt that surrounded it even when it could still be examined.

The geologist G.H. Kinahan described the stone in 1884, identifying it as stone C in his account of the Mongnacool rock art. He noted it was roughly square in form, lying flat, and composed of what appeared to be quartz-rock or quartzose-granite. His description of the markings was notably cautious: they had, in his words, "not a very ancient look", being shallow and indistinct, though he allowed they might be ancient. The eastern cup was unsymmetrical, deeper near its north-eastern edge, while the hollow to the south-west was rectangular in form and undercut. Kinahan even raised the possibility that the eastern cup was an original prehistoric feature that had been subsequently modified, perhaps by a later hand with a different purpose or no particular purpose at all. When the location he specified was revisited over a century later, in 1990, the stone could not be found.