Two low stone banks, set roughly 2.7 metres apart, enclose a circular area approximately 27 metres across, positioned on a slight mound at the south-western end of a ridge. When surveyors encountered it in 1942, they could not quite decide what they were looking at: possibly a small fort, possibly a folly, though there was no sign of a summerhouse or any other structure that might have explained its purpose. What made it stranger still was that, despite sitting in a prominent position with what was probably once a good view to the south and west, it appeared on no edition of the Ordnance Survey six-inch maps as anything deserving of antiquarian attention.

The 1942 surveyors were working without the benefit of the cartographic analysis that would eventually settle the question, at least provisionally. A tree-ring, in the designed landscape sense, is an ornamental circular planting of trees arranged around a central clearing or mound, a feature associated with 18th and 19th century estate landscaping across Ireland and Britain. The same Ordnance Survey maps that ignored the feature as an antiquity did record a network of pathways running through Glaskill Wood, suggesting the wood itself was laid out deliberately rather than left to grow wild. Taken together, the evidence points toward a 19th century ornamental origin, the circular stone banks serving as a kerb or boundary for a planted ring of trees rather than as the walls of any defensive or ritual structure.