One mile and a half east of Amroth a small valley which opens on the coast of Carmarthen Bay at Marros shows drift deposits of much interest. The valley itself is noteworthy. Like several others in the vicinity it is deeply cut in comparison with its width; the gradient of the valley sides is as high as 1 in 2, and the depth below the bordering hills is not less than 300 feet. The stream, which now drains the valley, rises on Marros Mountain, barely 2 miles from the shore, and flows down the main dip-slope of the Coal-measures, which here are greatly disturbed by folds and faults.