Summary of site:
The Kilskeery Group of the Carboniferous period in this part of Fermanagh consists of three formations. Bottom to top, these are: the Topped Mountain Sandstone, at 1000m enormously thick; the Ballyreagh Conglomerate, 350m thick; and the Ballinamallard Mudstone, also 1000m thick. This account describes one division of the Topped Mountain Sandstone, the Coolcran Conglomerate Member, important because it yielded a flora of microscopic spores that provided important dating evidence.
About 200m below the top of the Topped Mountain Formation there are 20m of conglomerates and massive, flaggy sandstones, exposed in a deeply incised stream valley. They form the stratotype (see glossary) of the Coolcran Conglomerate Member. A series of waterfalls identifies the section where the basal bed consists of 3m of conglomerate with lava cobbles up to 12cm across. Not far above this level, a 7cm thick, green, mica-rich shale occurs and it is this horizon that has yielded the plant spores. Eleven species have been identified and they typify two spore zones that include the whole of the Asbian stage and the early part of the succeeding Brigantian of the Carboniferous period. The time spanned is from 340 to 335 million years ago.
The sand-dominated sediments of the Topped Mountain Formation accumulated in a large land depression, probably in near desert conditions, throughout the Asbian. The Coolcran Conglomerate was a short-lived phase in this accumulation. Without evidence of plants in the immediate area, one can only speculate on the source of the spores but they were presumably washed in by brief rains.
The Kilskeery Group was considered to be unfossiliferous and thought to belong to the Devonian period as recently as the 1980s. The discovery of the spores was therefore crucial evidence in the largest revision of the Irish geological map in the late twentieth century. The site is a key component in the understanding and interpretation of the rocks of this area and an essential component of the geological history of Northern Ireland.