Wednesday, 24 February 2010

Point of contention

James Hutton is a geological hero. He was a doctor and chemist in late 1700s Edinburgh who had a fascination for all things scientific. One of his more important realisations was about the formation processes of rocks, and subsequently the lengths of time that would be needed for them to have formed, eroded and finally display their stratigraphic relationships visible today. This was not an easy subject to bring up at the time and he was condemned by many for what were seen as heretical and atheistic views.

He merits more than one post of his own, but what I wanted to mention today was a place, not a person. On Monday an American customer told me he'd just visited Siccar Point, and was clearly excited about it. Siccar Point is a promontory a little over a mile to the East of Pease Bay near Cockburnspath. Very close to the A1, and not hard to find. It's not a particularly noteworthy place to look at, but it holds a special place in geological history as it was where, in 1788, James Hutton and a couple of friends used a distinct unconformity in the rock layers to show how rocks could not have been laid down in rapid succession. Such as in a big flood, for example. At Siccar Point, slanted red sandstone strata from the Devonian, roughly 345 million years old, lie directly on top of the almost vertical Silurian grey, gritty sandstones (known at the time as 'schistus', but actually greywackes) that are 80 million years older. The exact datings were not known at the time, but the succession neatly shows some considerable period of time had elapsed between the deposition of the two series of rocks. Time enough for the lower set to have been drastically tilted from the horizontal and then worn down.

'Hutton's Unconformity' doesn't just refer to the beds at Siccar Point, but to all those he had identified. There are a number of them around Scotland, but Siccar Point is a bit of a favourite. Hutton viewed it from a boat, but if you're feeling brave enough, you can grab hold of the fixed rope and lower yourself down from the top of the cliff to examine a world-famous geological landmark for yourself.

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