Knockan Crag
Encyclopedia
Knockan Crag is a line of cliffs in Assynt
, Scotland
21 kilometres (13 mi) north of Ullapool
. The name is an anglicisation of the Gaelic
Creag a' Chnocain meaning 'crag of the small hill'.
The Moine Thrust
runs through the crag and there is a small visitor centre providing interpretation and artwork that explains the background to the 'Highlands Controversy' concerning the geology of the area.
and Archibald Geikie
on the one hand and James Nicol and Charles Lapworth
on the other. This was finally resolved by the work of Ben Peach
and John Horne
whose 1907 paper on the subject remains a classic text.
The main issue was that the Moine
schist
s at the top of the crag appeared to be older than the Cambrian
and Ordovician
rocks such as Durness
limestone
lower down. Murchison and Geikie believed the sequence was wrong and that the Moine schists must be the younger rocks. The conundrum was explained by the action of a thrust fault
- this being the first to be discovered anywhere in the world. The older rocks had been moved some 70 kilometres to the west over the top of the younger rocks due to tectonic action.
A monument to Peach and Horne's work was erected by the international geological community at Inchnadamph
a few miles to the north.
Knockan Crag National Nature Reserve
is part of the North West Highlands Geopark
, inaugurated in 2004 and part of the International Network of Geoparks
.
There is a visitor interpretation centre, and various walks along the crag explaining the features and including artwork such as 'The Globe' by Joe Smith.
s in the area.
Assynt
Assynt is a civil parish in west Sutherland, Highland, Scotland – north of Ullapool.It is famous for its landscape and its remarkable mountains...
, Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
21 kilometres (13 mi) north of Ullapool
Ullapool
Ullapool is a small town of around 1,300 inhabitants in Ross and Cromarty, Highland, Scotland. Despite its small size, it is the largest settlement for many miles around, and is a major tourist destination of Scotland. The North Atlantic Drift passes by Ullapool, bringing moderate temperatures...
. The name is an anglicisation of the Gaelic
Scottish Gaelic language
Scottish Gaelic is a Celtic language native to Scotland. A member of the Goidelic branch of the Celtic languages, Scottish Gaelic, like Modern Irish and Manx, developed out of Middle Irish, and thus descends ultimately from Primitive Irish....
Creag a' Chnocain meaning 'crag of the small hill'.
The Moine Thrust
Moine Thrust Belt
The Moine Thrust Belt is a linear geological feature in the Scottish Highlands which runs from Loch Eriboll on the north coast 190 km south-west to the Sleat peninsula on the Isle of Skye...
runs through the crag and there is a small visitor centre providing interpretation and artwork that explains the background to the 'Highlands Controversy' concerning the geology of the area.
Geological significance
During the 19th century prominent geologists conducted a prolonged and bitter debate about the fault line exposed here. The argument was primarily between Roderick MurchisonRoderick Murchison
Sir Roderick Impey Murchison, 1st Baronet KCB DCL FRS FRSE FLS PRGS PBA MRIA was a Scottish geologist who first described and investigated the Silurian system.-Early life and work:...
and Archibald Geikie
Archibald Geikie
Sir Archibald Geikie, OM, KCB, PRS, FRSE , was a Scottish geologist and writer.-Early life:Geikie was born in Edinburgh in 1835, the eldest son of musician and music critic James Stuart Geikie...
on the one hand and James Nicol and Charles Lapworth
Charles Lapworth
Charles Lapworth was an English geologist.-Biography:He was born at Faringdon in Berkshire and educated as a teacher at the Culham Diocesan Training College near Abingdon, Oxfordshire. He moved to the Scottish border region, where he investigated the previously little-known fossil fauna of the area...
on the other. This was finally resolved by the work of Ben Peach
Ben Peach
Benjamin Neeve Peach, FRS was a British geologist.He was born at Gorran Haven in Cornwall to Charles William Peach, an amateur British naturalist and geologist. Ben was educated at the Royal School of Mines in London and then joined the Geological Survey in 1862 as a geologist, moving to the...
and John Horne
John Horne
John Horne was a Scottish geologist. He was elected a Fellow of the Royal Society in 1900. He was a pupil of Ben Peach....
whose 1907 paper on the subject remains a classic text.
The main issue was that the Moine
Moine Supergroup
The Moine Supergroup is a sequence of Neoproterozoic metamorphic rocks that form the dominant outcrop of the Scottish Highlands between the Moine Thrust Belt to the northwest and the Great Glen Fault to the southeast. The sequence is metasedimentary in nature and was metamorphosed and deformed in a...
schist
Schist
The schists constitute a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is...
s at the top of the crag appeared to be older than the Cambrian
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
and Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
rocks such as Durness
Durness
Durness is a huge but remote parish in the northwestern Highlands of Scotland, encompassing all the land between the Moine to the East and the Gualin to the West...
limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
lower down. Murchison and Geikie believed the sequence was wrong and that the Moine schists must be the younger rocks. The conundrum was explained by the action of a thrust fault
Thrust fault
A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...
- this being the first to be discovered anywhere in the world. The older rocks had been moved some 70 kilometres to the west over the top of the younger rocks due to tectonic action.
A monument to Peach and Horne's work was erected by the international geological community at Inchnadamph
Inchnadamph
Inchnadamph is a hamlet in Assynt, Sutherland, Scotland. The name is an anglicisation of the Gaelic name Innis nan Damh meaning 'meadow of the stags'...
a few miles to the north.
Visitor Centre
National Nature Reserves in Scotland
National Nature Reserves in Scotland are established by Scottish Natural Heritage. Until 2004 there were 73 National Nature Reserves in Scotland, as per the list below...
is part of the North West Highlands Geopark
North West Highlands Geopark
The North West Highlands Geopark is a geopark in the Scottish Highlands. Awarded UNESCO geopark status in 2004, it features some of the oldest rocks in Europe, around 3,000 million years old...
, inaugurated in 2004 and part of the International Network of Geoparks
International Network of Geoparks
The Global Geoparks Network is a UNESCO programme established in 1998. Managed under the body’s Ecological and Earth Sciences Division, the GGN seeks the promotion and conservation of the planet’s geological heritage, as well as encourages the sustainable research and development by the concerned...
.
There is a visitor interpretation centre, and various walks along the crag explaining the features and including artwork such as 'The Globe' by Joe Smith.
Wildlife
There is a population of stonechats living near the visitor centre and ravenRaven
Raven is the common name given to several larger-bodied members of the genus Corvus—but in Europe and North America the Common Raven is normally implied...
s in the area.
External links
- Knockan Crag National Nature Reserve - official site