A shortish walk up to Cliff Rigg, to the great hole left from the extraction of whinstone in the 19th-century.
The whinstone is from a dyke, about 25m wide, of igneous rock that was injected through the local sedimentary strata about 59 million years ago, originating from a volcano centred on the Island of Mull in Scotland.
During the past 2 million years, ice sheets have toed and flowed across the dyke leaving deposits of till, or boulder clay, mostly on the lower ground of the Tees plain. At Cliff Rigg, the dyke, being harder and more resistant to erosion by the ice, forms the familiar ridge.
Whinstone is a very hard rock and has been much quarried and mined being used for road making and cobble setts.
The pinnacle of rock is termed a ‘scab’ of poor quality rock, left to prevent collapse of the sedimentary shales.
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