The Old Red Sandstone can be seen in a splendid, almost continuous section along the river both below and above the village. About 660m upriver from the village of Cadamstown the lowest beds of the Old Red Sandstone are beautifully exposed in a 12m high cliff section. Upstream from this cliff the contact between the Old Red Sandstone and the underlying Silurian rocks is exposed, and above this the Silurian rocks themselves are well exposed in the river bed.

If you follow the river downstream from the village you will eventually reach the point where the Old Red Sandstone is overlain by the lowest shales of the succeeding Lower Carboniferous period of earth history.

The glens that radiate out from Slieve Bloom are post-glacial in age. The new streams first cut through the deep blanket of soft glacial till and then exploited lines of weakness in the underlying rock, removing loose blocks and tending to follow the prominent joints in the bedrock.