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Siccar Point

Accorded Site of Special Scientific Interest status in 1961, the Siccar Point unconformity (known as Hutton's Unconformity') is an internationally famous place of geological pilgrimage. It is of great historical importance in the development of the science of geology.

In 1788, James Hutton first understood the significance of the geological structure at Siccar Point. Although not the first unconformity he had observed, it is certainly the most spectacular. The near vertical Llandovery (Silurian) age greywackes and shales are covered unconformably by gently dipping Upper Devonian or Lower Carboniferous red breccia and sandstones.

Hutton used the locality to demonstrate the cycle of deposition, folding, erosion and further deposition that the unconformity represents. He understood the implication of unconformities in the evidence that they provided for the enormity of geological time and the antiquity of planet Earth, in contrast to the biblical teaching of the creation of the Earth.

Siccar Point - the classic view of Hutton's unconformity. © Con Gillen, Edinburgh University.

A casting of the Siccar Point unconformity is housed in the American Museum of Natural History in New York.

Playfair wrote of Siccar Point in 1805: "On landing at this point, we found that we actually trode on the primeval rock, which forms alternately the base and the summit of the present land. It is here a micaceous schistus, in beds nearly vertical, highly indurated, and stretching from south-east to north-west. The surface of this rock runs with a moderate ascent from the level of low-water, at which we landed, nearly to that of high-water, where the schistus has a thin covering of red horizontal sandstone laid over it; and this sandstone, at the distance of a few yards farther back, rises into a very high perpendicular cliff. Here, therefore, the immediate contact of the two rocks is not only visible, but is curiously dissected and laid open by the action of waves."

Further reading:

Barclay, W.J., Browne, M.A.E., McMillan, A.A., Pickett, E.A., Stone, P. and Wilby, P.R. (2005) The Old Red Sandstone of Great Britain, Geological Conservation Review Series, No. 31, Joint Nature Conservation Committee, Peterborough, 393 pp.