For many years the New Red Sandstone of the Vale of Clwyd was shown upon the maps as resting generally on Carboniferous Limestone, but frequently overlapping it so as to pass on to the surrounding Silurian strata. No faults were indicated, and the structure of the Vale, as represented, suggested that a pre-Triassic syncline here existed, within which a remnant of Carboniferous rocks had been preserved from denudation and which had formed a bay in the Triassic coastline.