Welsh Journals

A Limestone Feature at Nicholaston by W. J. CHAMBERS LIMESTONE is a soluble rock. The limestones of Gower are well-bedded and jointed and therefore water moves easily within the mass. The con- tinuous movement of slightly acidic (aggressive) water causes the solution of rock and the formation of characteristic limestone features. One such feature, mentioned by E. M. Bridges in Gower XXI, occurs in several places at Nicholaston. These features are the 'sink holes' or 'swallets' which occur adjacent to the south Gower road. All are visible from the road but are to be found in private farmland (see fig. 1). Sinks are places where surface streams disappear into the ground, generally as a result of continuous solution. The best known examples are found in Yorkshire at Gaping Ghyll and Alum Pot. However, locally, Daw Pit in the Bishopston valley is well-known (see D. P. Ede 1972). The sinks here described are much smaller, the largest at Blind Pot being 25 feet deep. The Nicholaston sinks occur almost immediately the streams leave the Old Red Sandstone of Cefn Bryn and reach soluble limestone; they take the form of circular or elongate depressions with a hole which takes the water into the ground. It is interesting to note the surface continuation of shallow dry valleys downstream of the sinks especially below Blind Pot and Church Sink. These dry valleys were probably the courses of the stream before the development of the modern sinks, and where they meet the old chffline from deep Fig. 1. To show location of features mentioned in the text.