Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay
Location: 55o 55' 54" N, 002o 18' 04" W.
James Hutton, an early pioneer of geology, was puzzled by two different groups of rocks in Scotland. Around Edinburgh the rocks were nearly horizontal, although slightly folded and disturbed. Further south the rocks were intensely disturbed. He wondered what their relationship was. One day in 1788, he and some friends rented a boat and sailed along the coast, discovering the rocks here at Siccar Point. The younger sandstones are resting atop vertical beds of older rock. The older rocks must have been deposited horizontally, tilted, eroded, then buried by the younger rocks.
The vertical rocks are now known to be about 425 million years old and were deposited during the Silurian Period. They were tilted during a mountain-building event caused by the collision of North America and Europe. In North America the collision created the northern Appalachians. In Europe it is called the Caledonian Orogeny (Caledonia is the old Latin name for Scotland.) The mountains were eroded flat and the younger rocks were deposited during the Devonian Period about 345 million years ago, about 80 million years later.
Geologists seek out locations where rocks can bee seen in direct contact because those localities, called contacts, are places where the historical relationships of the rocks can be directly observed. The contact at Siccar Point is called an angular unconformity, a place where an interval of geologic time is not preserved, and where the lower rocks have been tilted so they form a sharp angle with the overlying rocks. Hutton's Unconformity at Siccar Point is one of the most spectacular examples in the world as well as being of great importance in the history of geology.
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Created 19 July 2009, Last Update 15 January 2020