Whether this was a matter of economy, a change in the workforce mid-construction, or simply the pragmatic thinking of a builder who knew that particular arch would catch less attention, nobody recorded. The discrepancy is small but telling, the kind of detail that gets smoothed over in later restorations and forgotten entirely unless someone looks closely.

The bridge at Coolacoosane carries a road over the Brogeen River, running roughly north to south, and was built sometime around the late eighteenth or early nineteenth century. It measures 6.5 metres in width and is constructed from random-rubble sandstone, the walls built from unshaped stones laid without a regular coursing pattern, a common and practical approach in rural bridge-building of the period. Four semicircular arches carry the structure, with pointed cutwaters, the angled projections on the piers that deflect the river current and reduce pressure on the stonework during floods. A vertical stone coping runs along the top of the parapet walls. The bridge sits adjacent to Brogeen Mill, suggesting this was once a working corner of the landscape, the road and the crossing serving the needs of a local milling operation as much as general traffic.