This quarry forms part of the stratotype of the Shanmullagh Formation, among the earliest Devonian rocks in Ireland. Key Site 1150 (Shanmullagh Formation; stratotype localities) gives the general picture. There are no major bedding planes in the 10m of rock visible in the quarry but laminations (beds a few millimetres thick) are present throughout. The rocks are fine grained, red-brown sandstones, siltstones and chocolate brown mudstones, the last showing ripples. The odd angular, coarse quartz grain can be found anywhere in the succession. The presence of feldspar in the sandstone is an indicator of rapid burial because exposed feldspars are unstable and quickly weather to clay minerals and quartz.
As at the other stratotype, desert conditions with seasonal salt-rich lakes predominated. The presence of ripple marks, common above the top of the quarry, show that the water was shallow and their orientation reveals a complex of flow directions.
