Walks in Silverdale and Arnside. Brian EvansЧитать онлайн книгу.

      The cave at Silverdale Cove (Walk 2)

      The last Ice Age, which ended around 15,000 years ago, left its mark on the area. Ice sheets scoured the rocks, resulting in sheets of smooth limestone that can be seen in many locations. A considerable thickness of ice covered the area, and as this melted Morecambe Bay covered a much larger area than it does now. It is thought that ice in the Irish Sea may have dammed the freshwater rivers to make Morecambe Bay into a gigantic lake. The present-day basins were submerged, and it is easy to visualise the Arnside and Silverdale hills as islands. The fluctuations in sea level left deposits of sediments or alluvium in the flat basins, giving rise, where well drained, to rich farmland, or forming the marshy areas such as Leighton Moss and Hawes Water. Around Hawes Water the substance diatomite can be found, which is made up of the siliceous fossil remains of microscopic organisms. It is a valuable commodity, used for its insulating properties, and was worked commercially at Kentmere in the Lake District.

      Hollows formed by large pockets of melting ice or slow drainage are typical of limestone scenery. These hollows are called dolines, and sometimes have a water sink at the base. Hawes Water lies over several merged dolines, and the doline hollow in Deepdale is the result of a collapsed cave. The larger basins, such as the area now covered by Hale Moss, were once lakes and still flood in winter and in wet weather. The edges of the basins were sometimes lined by small cliffs, like the ones close to the road at the edge of Hale Moss. These cliffs are riddled with small tubular water-worn passages. There is evidence of several sea levels along the Silverdale coast, and there is an almost perfect circular phreatic tube cave worn by water pressure action.

      The many limestone pavements in the area were scraped by ice and eroded by water and rainfall into their present form of clints – smooth surface blocks eroded over time – and grykes – the deep fissures between the clints. Solution pockets of varying sizes can also be seen on the surface where rainwater has created hollows by dissolving the limestone. Where the pavements are tilted, surface runnels are formed by water. These are especially pronounced on Farleton Fell and Hutton Roof Crags, where the rounded rundkarren are among the best examples in Britain. These were formed when the rocks were covered by a layer of vegetation and water draining away underneath the vegetation wore the limestone into its present attractive patterns. Sharp-edged rinnenkarren were formed where the rocks were open to erosion directly by the elements. These are rare in Britain and are best seen at The Rakes of Hutton Roof Crags.

      During the last Ice Age many limestone boulders were moved and deposited on other limestone beds, and there are many examples of these perched boulders, or erratics, in the area. (They are so called because they are not derived from the rock upon which they lie.) Sometimes the ice moved rocks from further afield before depositing them; Shap granite erratics can be seen on some of the walks.

      In geological time the limestone was covered by beds of red sandstone, long since removed by erosion. An interesting feature that developed at this time was caused by water seeping through the sandstone and becoming impregnated with minerals which were then deposited in the limestone caves below. This is explains the presence of copper and haematite (iron ore) which were mined in several parts of the area, especially at Crag Foot, where layers of brecciated sandstone filled the phreatic passages.