Smoo Cave is a very large sea cave, but the rear part is a karst cave
which formed inside limestones of the Durness Group.
Durness Group are layers of limestones and dolomites. The rocks were formed
during Odovician and Lower Cambrian as shelf sediments. They are found in a
narrow belt running north to south, from the area of the Smoo Cave to Ardarroch
at Loch Kishorn. The karst features of Smoo cave are typical for such a small
limestone area with impermeable and insoluble rocks surrounding it. Waters
flowing on impermeable rock, disappear in swallow holes as soon as they reach
the border to the limestone. They drain underground and reappear in karst
springs and caves. Such a cave river is to be found inside Smoo cave, water from
a burn which disappeared only a few meters away.
The cave is formed in a
band of Durness limestone which in turn is surrounded by quartzite, gneiss and
grits. Originally a small swallet cave, the entrance has been much enlarged by
the action of the sea.
The first chamber is the large
opening from the sea inlet and has been formed by the action of the sea. The
has been formed by the action of fresh water. The roof holes show the difference
in the forces that formed the caverns.
presence of caves in the vicinity of the Geodha Smoo,
indeed the presence of the Geodha itself, is a reflection of the character of
the local geology, which is
by Cambrian Dumess Limestone.
formed over many thousands of years, carved along
line of a weak fault, both by the river which today
through It and by the sea, which at times of high
still laps the back wall of the cave. The Inlet itself
created as the cave roof progressively collapsed with
deepening of the cavern (Gleed-0wen 1992).
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