This site is described as "stone circles" in Topographical Notes on the Barony of Coshlea, Co. Limerick, including Lackelly, the Lake District, Cenn Abrat, Claire, Tara Luachra, &c. by
P. J. Lynch (1920) RSAI
Rev Lynch, who from his paper I believe only viewed photos of the "circles" described them as follows ;
"The discovery of the stone circles on the eastern end of Slievereagh induced some writers to identify them as the remains of the residence or burial place of Olioll Olum." we skip on to "When I prepared the first plan of these circles I described them as probably two concentric circles outside the remains of a dolmen or cairn. I have given the question further consideration and changed my opinion somewhat. I have completed the outer circle (about 45 feet in diameter), when complete, could have rested within the "Benches" while the second "circle" and the stones inside of it, mark the base of a cairn about 26 feet in diameter, enclosing the tomb, of which the inner stones formed part.
There is no "Cromlech" (marked on OS Map) on the mountain. There are several blocks of stone resting on the rocky surface of the mountain; but as Dr. Fogerty writes "if a Cromleac is something built by human hands, there is none""
He then goes on to give a plan of the stone circles. If anyone has access to JSTOR you can find the plan here http://www.jstor.org/stable/25514569?seq=17.
However from looking at the remains up there I would say that the best these circles could be is the kerb of a cairn. Even at that most of the stones up here look to be naturally placed rather.
The notice board in Glenbrohane mentions that the "King's Chair" can be found amonst the rocks of the cairn. I'm not sure which stones they refer to but I've taken a photo of what I thought looked most chair like.
The walk to the top follows a marked path for a lot of it and then swings off on a forestry path up to the antena on top. Views from here are great into the plains of Limerick to the north.