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Rocks of NW Scotland - Stratigraphic Section

Stratigraphy refers to the way in which sedimentary rocks are laid down in sequence, one on top of the other. The diagram below shows the rocks of NW Scotland in order of age, youngest at the top, in a schematic stratigraphic section. The Moine schists have been omitted: they were probably deposited at about the same time as the Torridonian, but when that happened they were far away from their present position.

- Unconformity -

Cambrian Succession

Laid down in the sea

Durness: dolomitic limestone
Salterella Grit: impure sandstone with small shelly fossils
Fucoid Beds: dolomitic siltstone
Pipe Rock: quartz sandstone with vertical burrows
Basal Quartzite: quartz sandstone with cross bedding

Age 540 - 500 million years
Upper part of Durness limestone is Ordovician, less than 500 million years

Thickness of Basal Quartzite plus Pipe Rock is about 150 metres


Fractured limestone
Grey limestone

Salterella Grit 1
Salterella Grit 2 (fossils)

Fucoid Beds

Pipe Rock

Basal Quartzite


Marble 1
Marble 2

- Unconformity -

Torridonian Succession

Laid down mainly by rivers

Torridon Group
mostly red-brown sandstones
Age about 1000 million years
Thickness up to 6 kilometres

Stoer Group
Red-brown sandstone, conglomerate, mudstone
Age about 1200 million years
Thickness up to 2 kilometres


Torridon sandstone

Volcanic mudflow

Stoer sandstone

Stoer conglomerate

Lewisian Gneiss Complex

Mostly igneous rocks, folded and highly metamorphosed

Gneiss (pink) with granite sheets (red)
Age about 1750 million years

Gneiss (pink) with mafic dykes (green)
Age about 2700 million years


Laxfordian granite
Laxfordian gneiss

Scourie dyke

Felsic gneiss 1
Felsic gneiss 2
Mafic gneiss
Ultramafic gneiss

In addition to the links to individual rocks, you can visit the following places:

For the igneous and metamorphic rocks of the Moine Thrust zone, see:

Scourie Achmelvich Laxford Clachtoll Stoer Assynt Skiag Bridge Glencoul Knockan Borralan Ledmore
Home Geological History Stratigraphy Area map Rock Index About

D.J. Waters, Department of Earth Sciences, May 2003