According to the Archaelogical Inventory of County Carlow, item no. 317 at Rathgeran:
Enclosure (possible) Grass-covered bank of earth and stones, including some large slabs, several standing upright, curving W–N (C 52m; est. Diam of circle if complete c. 80m; enclosing summit of hill). 1-9-1987
Archaelogical Inventory of County Carlow.
The Government of Ireland (copyright)
ISBN 0 7076 0324 2
This site really needs to be properly surveyed and studied.