Hutton's Unconformity

Hutton's Unconformity is a name given to various famous geological sites in Scotland identified by the 18th-century Scottish geologist James Hutton as places where the junction between two types of rock formations can be seen. This geological phenomenon marks the location where rock formations created at different times and by different forces adjoin. For Hutton, such an unconformity provided evidence for his Plutonist theories of uniformitarianism and the age of the Earth.

In a search for such a juxtaposition, Hutton, accompanied by some of his friends, examined sea cliffs and found examples at several locations where the two rock types had been laid bare, the most famous being at Siccar Point.

Hutton hit on a variety of ideas to explain the rock formations he saw around him, and after some 25 years of work, his paper entitled Theory of the Earth; or an Investigation of the Laws Observable in the Composition, Dissolution and Restoration of Land upon the Globe was read to the recently established Royal Society of Edinburgh on March 7 and April 4, 1785.

Later that year Hutton read an abstract of Concerning the System of the Earth, its Duration and Stability to a Society meeting, and had it printed and circulated privately. In it, he outlined his theory that the "solid parts of the present land appear in general, to have been composed of the productions of the sea, and of other materials similar to those now found upon the shores."

From this he deduced that the land was a composition which had been formed by the operation of second causes in an earlier world composed of sea and land, with tides, currents, and "such operations at the bottom of the sea as now take place" so that "while the present land was forming at the bottom of the ocean, the former land maintained plants and animals; at least the sea was then inhabited by animals, in a similar manner as it is at present", and that most, if not all, of the land had been produced by natural operations involving the consolidation of masses of loose materials collected at the bottom of the sea, followed by the elevation of the consolidated masses to their present position.

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