Welsh Journals

THE BISHOPSTON VALLEY The beauty of Gower lies not only in its famous coastline, with its rocky cliffs and attractive bays, but also in the river valleys which slope to the sea. Attention has, however, been concentrated on the coast to the neglect of these valleys which, though few, are full of interest. Despite the high rainfall of the area, the number of streams in Gower is small. This is due to the nature of the peninsula which is floored mainly by limestone rocks broken by many joints. Water, instead of flowing to the sea along the surface, seeps down through these cracks until it reaches the level where the ground is completely saturated, with water filling all the fissures. This level is called the water-table." While falling through the air, rain absorbs a certain amount of carbon dioxide to become slightly acid, and these waters by dissolving the limestone widen the joints down which they pass. Because of thick beds, large channels and caverns may be formed by solution underground without danger of collapse, as in the Mendips and at Porth-yr-Ogof, so that rivers may flow underground for some distance. They become visible only where the roof has fallen in or where they emerge in a more normal river valley. Open valleys in limestone regions may be formed by the collapse of cavern roofs, but in Gower it seems likely that they were formed for the most part in the ordinary course of river development. The truncation of the steeply dipping rocks of much of Gower, by an even surface rising only gently from about 200ft. around the coast to a little over 300ft. inland, bears evidence to the fact that at one time the sea extended over this area. Normal sub-aerial and river erosion would not have cut so evenly across the different rock structures in the same regardless manner as the sea has done. As the sea retreated, rain falling on the emerging land gathered into streams which, since the water-table was near the surface, flowed across even the limestone areas. A continued retreat of the sea was accompanied by a fall in the level of the water-table inland, and many of the streams ceased to flow across the surface but went underground leaving their former valleys dry. They reappeared at the surface near the coast where the water-table was close to the surface. In these lower reaches the streams flowed normally and cut down in their valleys until the valley gradients sloped only gently towards the sea with just sufficient slopes to enable the rivers to carry along the load of rock rubble which was constantly slipping down from the valley sides. These streams gradually extended their open valleys further inland by cutting back and by the sapping of springs at their heads, capturing the drainage which had previously been underground. Many of these features may be seen in the Bishopston valley, where the stream has its headwaters on Fairwood and Clyne Commons