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A Brief Geological History of Silver Meadows by Alan Smith

The site of the Silver Meadows Reserve in the Embleton valley is a relict of the last ice age. A shallow lake left here when the ice retreated, gradually transformed into the wetland we have today.

At the glacial maximum (approx. 18,000 years ago) ice covered the whole landscape. Glacial erosion was concentrated in excavating out the Bassenthwaite Lake basin as the ice moved out of the Lakeland Fells north westwards on to the Solway Plain. It is difficult to estimate how much erosion ice achieved along the Embleton valley. Ice was clearly present, moving westwards, but the size and form of the valley pre-glacially is problematical.

As the ice melted away thick boulder clays were left over the landscape. Meltwater flushed sand and gravels into the valley floor. A bank of sands and gravel formed a natural barrier across the eastern end of the valley, effectively impounding the drainage. A shallow lake, draining eastwards towards Bassenthwaite Lake was left stranded here. Over the last 10,000 years of the post-glacial period, silt and sediments washing from the slopes and carried by streams have infilled the lake and converted it into the wetland of today. The growth of wetland vegetation has also contributed greatly to this process. It stands at around 75m OD, barely above the present level of Bassenthwaite Lake.

The bedrock and superficial geology is not visible on the reserve. The glacial sands forming the barrier at the eastern end form the slightly higher ground banked up against the prominent rocky hill of Castle How, across the road from the reserve entrance. Further west, along the Embleton Valley, other mounds of sand and gravel are visible near Naithwaite and beyond at Netherscale.

North of the A66 there is a much smaller wetland relict in the area between Dubwath and Ouse Bridge.

The high ground surrounding the reserve is made of dark grey siltstones and mudstones of the Skiddaw Group (approx. 500 million years old). The Embleton Valley in which the reserve lies may possibly have been an east-west pre-glacial valley. There have been suggestions that pre-glacially the River Derwent may have exited this way, but evidence for this is weak. There is undoubtedly a clear valley route this way, defined by the high ground formed of bedrock both to the north and south, but the structural grain here is naturally west-east and the topography may simply reflect the underlying geology. The present valley floor rises only slightly to around 100m, but the extent and depth of the glacial and alluvial materials is unclear. The lake that once lay over the present site was undoubtedly shallow (a few metres at most). It probably extended a little way further west than the reserve. Until coring of the site is done the depth of the peat, lacustrine sediments and glacial materials on the valley floor will not be known. 

                                                         Map showing Embleton and Dubwath area geology. (Copyright Alan Smith 2015)

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