Knockan Cliff Visitor Centre
Introduction
Perched above the road, sited under the cliffs of Knockan is a visitor
centre run by the Nature Conservency Council. The site, or at least the cliffs,
is one of major importance to the geological world and the displays and
associated Nature Trail give a comprehensive introduction to the surrounding
landscape. Being situated above the main road between Coigach and
Assynt, next to Lochan an Ais, it gives a comprehensive panorama
to the west towards Cul Mor,
Stac Pollaidh and
Ben Mor Coigach. The guided
trail is one of the more adventurous of its type as it climbs up the cliff-side
to the crest; the associated texts give you a choice between a study of the
local vegetation and a geological trail - or both. Along the top of the cliff,
embedded in the peat, you can see old tree stumps that are the remains of the
old Caledonian pine forests, dating back about 4,000 years. We called in at the
car park again in August 1998 on a very wet day in a somewhat futile hope that
the cloud might lift and the hills would return to view. In chatting to the
warden we discovered that some of the wooden decking on the cliff-top walk was
broken and that the trail had been closed to visitors. It seems that the
imposition of 'safety' becomes decidedly over-bearing and defeats the whole
objective of opening up the area to visitors. I hope that the authorities do
feel that they can open the trail again soon as it is one of the more memorable
in the country and well worth a visit by those not wishing to undertake a major
mountain expedition.
During our holiday in 2000 we passed Knockan Cliff and noticed that the
the centre has been closed pending a complete re-development. At the start of
August 2001 the signs for the centre were still under wraps and the site
closed. However it seems that it opened later in the month and a new site has
been launched giving a bit more detail at
www.knockan-crag.co.uk.
The geological interest in
Knockan is brought about by the unexpected bedding of the rocks in this region.
Usually beds of rock lie with the youngest layers on top, and the older rocks
below. Whilst buried under the later layers, the older rocks have been exposed
to high temperatures and pressures and hence have been significantly altered.
However at Knockan it is the upper layers, the dark grey schists forming the
crest of the cliff, that appear the most altered (and therefore actually the
oldest). It was only in 1859 that a Professor Nicol argued that the normal
sequence had been broken by a fault in the Earth's crust and that the older
rocks had been driven bodily over the younger layers. This form of geological
disruption created by the mountain building forces in the Earth's crust is now
generally accepted and can be found on all continents, but was contested at the
time. The fault at Knockan is now known as the Moine Thrust.
The Rocks of Coigach and Assynt
Lewisian Gneiss |
This is the oldest rock seen in Britain
formed by the recrystallisation of older rocks in the period 2,800 to 1,400
million years ago. This rock is below the surface at Knockan but around
Lochinver and along the coast the overlying rocks have been eroded to
reveal this the gneiss. The rock is extremely hard and produces an acid,
infertile soil; when crushed the rock is used in road-making and building. |
Torridonian Sandstone |
Over 800 million years old this rock is
the oldest unaltered sedimentary rock in Britain; it does not contain any
fossils as it pre-dates any animals with hard parts. The sandstone was laid
down in Precambrian times when the region was a desert and in this area is
about 600m thick. The mountains of
Cul Mor,
Ben Mor Coigach,
Stac Pollaidh,
Canisp and
Suilven are all built up of this type
of rock. The rock is weather resistant and is used as a building stone. |
Basal Cambrian Quartzite |
A white sandstone some 75 mtres thick laid
down under a shallow sea in the Cambrian period, 600 million years ago. The
rock gives the white appearance to the summits and eastern slopes of mountains
in the area and, being broken by frost, forms the screes on
Cul Mor and under Knockan
cliff. |
Pipe Rock |
92 metres thick, this rock is similar to
and lies over the Basal Quartzite; the fossil 'pipes' formed by the burrows of
ancient marine worms visible in the rock give it it's name. |
Fucoid Beds |
This rock is a fossil-bearing brown shale
that was also formed in a shallow sea. It is 15 metres thick |
Serpulite Grit |
A gritty quartzite 10 metres thick that
separates the the Fucoid Beds from the Durness Limestone. |
Durness Limestone |
Laid down in a clear sea at the end of the
Cambian period, 500 million years ago, the limestone can be up to 500 metres
thick in the Highlands. At Knockan the rock forms a narrow band at the
foot of the cliff, it also forms the lime-rich soil around Elphin
(readily identified by the rich green grass growing in place of the usual
heather) and the caves and disappearing
streams at Inchnadamph. |
Moine Schists |
These rocks probably originate from the
same time as the Torridonian Sandstone, 800 to 1,000 million years ago, but
have been deeply buried and recrystallised some 400 million years ago. A dark
coloured, banded rock formed by the effect of heat and pressure on sands and
muds which can be broken into slabs. These rocks now sit above the Durness
Limestone, a shift along the Moine Thrust that carried the rock some 20
kilometres, and forms the upper crest to Knockan cliff. |
References
- Geological Trail, Knockan Cliff. Nature Conservancy Council.
