Summary of site:
The Bundoran Shale Formation is important in the early Carboniferous rocks of the north of Ireland. In this stream bed the section through the formation exposes thin limestones composed of fragmented fossils and slightly thicker shaley limestones. Dark coloured lime-rich mudstones are also present. Near the top of the section the limestones thin and become discontinuous, breaking into nodular beds separated by mudstones over a metre thick. While there are some fossils here, they are not as plentiful as at other Bundoran Shale localities. Neither the base nor the top of the formation is seen at this outcrop.
It used to be thought that these rocks represented the transition between the Ballyshannon Limestone Formation, immediately below, and the Bundoran Shale but that interpretation is now discounted. All the rocks present are part of the Bundoran Shale Formation.
The rocks have been faulted and folded. One of the north-westerly trending faults has been intruded by molten rock of basaltic composition, forming a dolerite dyke. The temperature of this intrusion was high enough to fuse the mudstone walls into a tough, metamorphic (altered) rock called a hornfels. The folding takes the form of a broad down warp (syncline).