Some geology additions to the Buxton collections show volcanic events in the making of the local geology and gave a great excuse (as if one was needed!) to get out and explore to see where they came from. Some of the new specimens came from Cressbrook Dale, a dramatic limestone dale near Litton dominated at the top end by the imposing Peter’s Stone. At various times there’s been volcanic activity at a number of centres in the White Peak, which include Tunstead, Matlock, Alport and Eyam Edge. Not necessarily large volcanoes, these could have been areas of vents and fissures under the shallow sea that covered the area at the time, and from which lava flowed or material was ejected to produce falls of ash. This led to layers or intrusions of lava flow and tuff inside the limestone.
In Cressbrook Dale these outcrop where the rocks have been worn away.
The picture above shows the North end of Cressbrook Dale and another feature of limestone dales – the seasonal river produced by our recent heavy rains!
Standing above the valley on a cold, damp, windy January day, it takes a real leap of imagination to picture the area as it was over 300 million years ago – not here, but thousands of miles away near the equator, covered with a warm shallow sea. Could it have looked like this …?
Tuff is formed from volcanic ash blown out of vents, eventually settling on the sea bed. There’s evidence that the Litton Tuff was the result of at least two volcanic vents, one west of Tideswell and another under Bleaklow, which probably erupted repeatedly to build up a layer of material.
At Cressbrook Dale the tuff layer forms a ‘wayboard’ separated by a depth of limestone from a lower layer of lava. The picture below shows such a wayboard in Ecton Copper Mine, where the ash appears as a soft clay.
Hunter J. & Shaw R. 2011 The Cressbrook Dale Lava and Litton Tuff between Longstone and Hucklow Edges, Derbyshire. Mercian Geologist 17(4); 229-242.