Hutton's Unconformity
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Hutton's Unconformity is the name given to various famous geological sites in Scotland. These are places that were identified by 18th century Scottish geologist James Hutton as an unconformity, which provided evidence for his theories of Uniformitarianism and about the age of the Earth.
One such location is on the Isle of Arran in south-western Scotland, identified by Hutton in 1787. It occurs where some vertically oriented Dalradian schists are overlain by more recent (possibly Carboniferous) horizontal sandstone. The difference in dip between the two rock layers is particularly obvious when at the site.
Another is the 'angular unconformity' at Jedburgh (pictured).[1]
The best known may be at Siccar Point, Berwickshire. Here Silurian rocks have been tilted almost to the vertical. Younger Devonian rocks lie unconformably over the top of them, dipping gently, indicating that an enormous span of time must have passed between the creation of the two beds. When Hutton and James Hall visited the site in 1788 their companion Playfair wrote:[2][3]
| On us who saw these phenomenon for the first time the impression will not easily be forgotten...We felt necessarily carried back to a time when the schistus on which we stood was yet at the bottom of the sea, and when the sandstone before us was only beginning to be deposited, in the shape of sand or mud, from the waters of the supercontinent ocean... The mind seemed to grow giddy by looking so far back into the abyss of time; and whilst we listened with earnestness and admiration to the philosopher who was now unfolding to us the order and series of these wonderful events, we became sensible how much further reason may sometimes go than imagination may venture to follow. John Playfair (1805) Transactions of the Royal Society of Edinburgh, vol. V, pt. III.[4] |
[edit] See also
[edit] References
- ^ "In and Around Jedburgh..." jedburgh-online.org.uk. Retrieved 01 March 2008.
- ^ McKirdy, Alan Gordon, John & Crofts, Roger (2007) Land of Mountain and Flood: The Geology and Landforms of Scotland. Edinburgh. Birlinn. Page 253.
- ^ Gillen, Con (2003) Geology and landscapes of Scotland. Harpenden. Terra Publishing. Page 95.
- ^ John Playfair. Hutton's Unconformity (html). Transactions of the Royal Society of Edinburgh, vol. V, pt. III, 1805, quoted in Natural History, June 1999.
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