Ancient river deltas and swampy forests
During the early Carboniferous times (c.360-310 million years ago) Central Scotland was inundated by a shallow sea.
Rivers carrying sand formed a complex delta system, with variations in sea levels over time creating marine environments and swampy tropical forests. These changes in environments can be seen in the variety of rocks in the Nethan crags with sandstone, siltstone and mudstone (Photo A) with limestone and coal seams exploited in former workings (Photo B). The base of the sandstone bear abundant, well-preserved fossil tree-like Lycopod branches that were carried along and deposited by streams during floods (Photo C).
The Lower Nethan Gorge, through which the River Nethan enters the Clyde Valley at Crossford, formerly joined the Clyde Valley via a now infilled channel approximately 1.5km to the north near Overton. This was due to a postglacial cut in its original course, and the cutting of new valleys is a characteristic of the area. It is similar to what can be seen at the ‘Nemphlar channel’ at Auchenglen, Falls of Clyde, Mouse Water, Avon Water, Fiddler Burn and Garrion Gill.
There are bus stops and parking near the tourist information point at Crossford. The gorge can be accessed via a trail from Crossford Village, or from the car park at Craignethan Castle. The trail is a good path through woodland along the top of the gorge, with a viewpoint over the gorge nearer the castle. Public access to the gorge itself is not advised as the terrain is difficult and dangerous. However, you can still enjoy it with GeoCam below, narrated by British Geology Survey geologist, Katie Whitbread.
The geological sites and features of the Clyde and Avon Valley tell a dramatic story of the development of the landscape over 400 million years, from ancient sandy streams, river deltas, swampy forests and glaciers. The rocks and rivers of this story shaped the heritage, and remain a source of power, havens for woodland and wildlife, and places of recreation and creative inspiration today.
Travel through time to reveal the hidden history in the rocks and landforms by exploring the other ‘Shaping the Landscape’ museum items below, and visiting the Shaping the Landscape Exhibition at New Lanark. Read the full report by clicking on the ‘Shaping our Landscape Trail Report’ link under ‘Find Out More’, or below. Whilst many ‘Shaping the Landscape’ sites are accessible to walkers, some sites are inaccessible, but featured as museum pieces to help demonstrate the development of the Clyde and Avon Valley.