A fault divides the latter from the mass of red-brown Old Red Sandstone that spreads south nearly to Enniskillen.
A few Devonian forms have also been recorded from the Parry Archipelago, and Nathorst has shown the existence of Old Red Sandstone facies of Devonian in Traill Island, Geographical Society Island, Ymer Island and Gauss Peninsula.
Under powers secured in 1884, the town obtains its chief water supply from a gathering ground near the sources of the Taff on the old red sandstone beyond the northern out-crop of the mineral basin and on the southern slopes of the Brecknock Beacons.
The colour is usually red, forcibly recalling the Old Red Sandstone and Trias of England.
It has some similarity to the Old Red Sandstone of Great Britain.
