Geological history | ||
Three hundred and fifty million years, the area which is now the Yorkshire dales was made up of grits, slates and shales, covered by a shallow sea in a land mass close to the equator. Over time, extra deposits were laid down on this base rock, the lowest of which was Great Scar Limestone, or Mountain Limestone. Formed under great pressure from the shells and bodies of ancient sea-living organisms, this grey-white limestone is fine grained, and characteristic of the central and southwestern dales - it is clearly seen, for example, at Gordale Scar and Malham Cove in Malhamdale, and Kilnsey Crag in Wharfedale.
As the land drifted north, the sea became shallower and a delta was formed, laying mudflats or sediments of shales, sandstones and limestones over the Great Scar limestone which make up the rocks known as the Yoredale Series, most noteable in Wensleydale (the area around the River Yore). As limestone erodes more slowly than the other rocks, this dale is scattered with white outcrops of stepped limestone scars, and filled with waterfalls powered by water filtering through the porous rock and tumbling down natural staircases.
After a period, coarse-grained sandstones and bands of shales were deposited in the widening delta, leaving a layer of Millstone Grit over the Yoredale Series, prominent in much of the eastern dales. This grit also caps peaks such as Ingleborough (near Ingleton in the western Dales) and Whernside (off Dentdale), giving them their distinctive flat tops.
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