About the stone

Torridonian Sandstone          Tarradale Sandstone            Caithness Flagstone

Torridonian Sandstone

Loch Dubh Masonry is able to offer a selection of building stones from the Highlands and Islands, including reclaimed Torridonian sandstone.

Liathach - King of the Torridonian hills
Liathach – King of the Torridonian hills
Geology of the Torridonian

The Torridonian sandstones are the oldest sedimentary rocks in the British Isles, deposited atop the metamorphic Lewisian but preserved only in the Caledonian foreland of NW Scotland. Their presence tells of the erosion of long-gone mountain ranges and of ancient landscapes. Within the the Torridonian are at least two distinct packages of sediments. The main sequence is called the Torridon Group, which attains an estimated thickness in excess of 6 km. The lower part of this Group (the Applecross Formation, named after its type area in Wester Ross) is the classical pebbly sandstone that forms the cliffs and scarps of some of the iconic hills in the NW Highland such as Liathach and Suilven. Beneath the Torridon Group lies a second sequence of older sedimentary rocks, known as the Stoer Group. These are classically lumped in with the rest of the Torridonian, and reaching thicknesses in excess of 3 km. Torridonian outcrops are shown in the figure below.

Map of the Foreland of the NW Highlands showing main rock types
Map of the Foreland of the NW Highlands showing main rock types

Where and how were the Torridonian Rocks deposited?
Work in the latter part of the 20th century has gradually established that the Torridonian Rocks were deposited within sedimentary basins controlled by normal faults. The sediments were deposited dominantly by rivers, but they also record other continental. One of the most dramatic features of much of the Torridonian outcrop is the basal unconformity with the Lewisian basement. This represents elements of the ancient landscape, and preserves low hills and valleys. Up to 600m of the topographic relief present in the ancient landscape is preserved in Wester Ross. The Torridon Group has been extensively studied to determine the palaeo-flow direction of the rivers that deposited the sediments, together with evidence for the likely source of the material. The data suggest that the Torridon Group was deposited on very large alluvial fans, perhaps 50 km across, fed from source areas to the west, beyond the modern Outer Hebrides. It is likely that much of the material was derived from a combination of Laurentian shield material (now buried on the continental shelf) and recycled older sediment.

The ages of Torridonian rocks
Dating sediments is particularly difficult – especially when they are essentially unfossiliferous. We know that the Stoer is younger than the basement that they overlie – which makes it younger than about 1400 million years old. Thin limestones within the Stoer Group have yielded radiometric ages of about 1200 Ma, and the best guess is that the Torridon Group was deposited atop it about 1000 million years ago. In summary, the Torridon Rocks are actually two distinct sequences separated by an unconformity representative of a significant time gap – perhaps as much as 200 million years. From palaeomagnetic data it is estimated that the palaeolatitude of the Stoer Group at the time of deposition was about 15 degrees from the equator. The Torridon Group on the other hand records palaeolatitudes of about 42 degrees from the equator. The significant time period between layers is consistent with the time needed the plate motion to take what would eventually become NW Scotland through this great distance.

source: http://www.see.leeds.ac.uk/structure/assyntgeology/geology/rock_sequence/torridonian/

The Torridonian as a building stone

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Tarradale Sandstone

Loch Dubh Masonry is pleased to offer a wide range of reclaimed dressed Tarradale sandstone.

Geology of Tarradale Sandstone

The old Tarradale quarry is situated a couple of kilometres east of Muir of Ord on the Black Isle. The rock type here is the Raddery Sandstone Formation, part of the Black Isle Sandstone Group, mid Devonian in age (385-398 million years old). These rocks were formed from rivers depositing mainly and gravel detrital material in channels to form river terrace deposits, with fine silt and clay from overbank floods forming floodplain alluvium.

(source: http://mapapps.bgs.ac.uk/geologyofbritain/home.html)

Tarradale Sandstone as a building stone

Tarradale sandstone has been used extensively in buildings throughout the Highlands over the last couple of centuries. As a distinctively red freestone it proved very popular for large public buildings such as Inverness Castle, as well as being used widely for estate houses throughout Ross-shire in Victorian times.

Inverness Castle built using Tarradale Sandstone
Inverness Castle built using Tarradale Sandstone

Browse currently available Tarradale Sandstone by clicking on the links below for more information:

  • Skews Price: Available upon request
  • Mullions Price: Available upon request
  • Rybats Price: Available upon request

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Caithness Flagstone

Loch Dubh Masonry is pleased to offer a wide range of bespoke Caithness Flagstone products.

Geology of Caithness Flagstone

Much of Caithness is underlain by Middle Devonian flagstones, thinly-bedded siltstones and sandstones. These cleave to give sheets which have used extensively in the past as paving, tiles and field boundaries. These sedimentary rocks were laid down around 370 million years ago in a huge Orcadian lake. The sedimentation was rhythmic – the cycles are repeated again and again in layers of rock with a cumulative thickness of about 4 km. Sequences within the cycles represent the lake’s responses to changes in: rainfall, evaporation, wave action and desiccation.

Caithness Flagstone
Caithness Flagstone

source: http://www.landforms.eu/Caithness/geology.htm

Caithness Flagstone as a building stone

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Beautiful Highland Stone