Just below the surface, and in places visible at the shore, lies a dense layer of oyster shells between 30 and 40 centimetres thick, packed into a matrix of dark soil. This is a midden, the accumulated refuse of people who gathered, opened, and ate shellfish here over an extended period, discarding the shells in such quantities that they have effectively become part of the landscape itself. What makes the site at Ballinlig unusual is not just its scale but its persistence: it never appeared on any edition of the Ordnance Survey six-inch maps, leaving it largely unacknowledged on the official cartographic record despite being physically present along nearly the entire eastern coast of the peninsula.

The greatest concentration of material gathers at a D-shaped projection of land at the south-east of the peninsula, where the site takes on a more legible shape. Here, a lens of shell and dark soil is visible at the shoreline, and roughly 45 metres back from the water sits a naturally occurring pool. In the ground between the shore and that pool, midden material is present in large quantities, with the densest accumulation, measuring approximately 50 metres north to south and 30 metres east to west, lying adjacent to the eastern edge of the pool. At the north-east of the peninsula, the shell layer is sandwiched between a covering of sand above and a stony subsoil beneath, suggesting that natural processes of deposition and erosion have been working over and around the site for some time. The site was recorded by Synge in 1985, offering at least a baseline description of what the coastline holds just beneath its surface.