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You are here > Home > Out & About > Classic
Sites:
Arran
- Hutton's Unconformity
(Other classic sites on Arran include Judd's
Dykes)
The Isle of Arran has been a Mecca for geologists for many years due to its
wonderfully varied geology. Even in the early days of geological exploration,
the likes of James
Hutton and Sir
Archibald Geikie were attracted to its rugged slopes and coastline. It
was here at Lochranza in particular that Hutton first found evidence that supported
his 'Uniformitarianism' theory - that the Earth was much older than previously
thought. Here, gently dipping layers of sedimentary rocks are seen to overlie
steeply dipping metamorphic rocks. To Hutton's eyes, the basal rocks had a
history much older than the overlying rocks. He proposed that they had been
created, deformed, uplifted and eroded, whereupon they were then overlain by
sediments deposited in the sea to create the younger rocks. This whole unit
must then have been uplifted to its current position for the process of erosion
to begin again. Hutton correctly perceived that this could only have happened
over an incredibly long period of time. This became one of several unconformities that
Hutton identified. Siccar
Point is perhaps his most famous.
Hutton's Unconformity - Laggan Site of Special
Scientific Interest on the north coast of Arran is the site of another
unconformity discovered by James Hutton. © Scottish Natural Heritage.
The basal metamorphic rocks consist of Dalradian schists that dip steeply
to the southeast. These schists are Precambrian in age. The unconformably overlying
sedimentary rocks come from a thick sequence of cornstones in the Kinnesswood
Formation of the Inverclyde Group (Lower Carboniferous). The beds of this formation
dip gently to the northwest.
Further reading:
Arkley, S.L.B. (2005) North Newton Shore, Isle of Arran. In The Old Red
Sandstone of Great Britain (Barclay, W.J., Browne, M.A.E., McMillan, A.A.,
Pickett, E.A., Stone, P. and Wilby, P.R.), Geological Conservation Review
Series, No. 31, Joint Nature Conservation Committee, Peterborough, pp.
192-195.
McKerrow, W.S. & Atkins, F.B. 1989. Isle of Arran - A Field Guide for
Students of Geology. 2nd edn. The Geologists' Association, London.
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