Cailleach Head

Site of Special Scientific Interest · 57.9303, -5.4052

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Also within

Ross and Cromarty County

Condition (NatureScot)

Favourable (1)
UnitFeatureConditionArea (ha)Assessed
F1 Torridonian Favourable — 2008-11-18

Habitats

Fast flowing river and stream

Geology & landscape

Rock Type: Shale

Landscape processes: Fluvial

Description

CAILLEACH HEAD Cailleach Head Site of Special Scientific Interest (SSSI) lies in Wester Ross, 15km northwest of Ullapool and 2km northwest of Scoraig. This nationally important site comprises the ‘Cailleach Head Formation’, which represents the youngest known Torridonian rock sequence. Torridonian rocks were deposited between 1 billion and 800 million years ago, in a semi arid to sub-tropical environment. The site is important because of the exposures of rhythmic alterations of sediments, known as ‘cyclotherms’. This is one of the best exposed sequences of such cyclotherms in Britain. The sedimentary sequence at Cailleach Head includes sandstones, siltstones and dark coloured shales. Some of the sandstones contain sedimentary structures such as ripple marks, indicating deposition in shallow running water. There are 20 dark shale and silt sequences, interspersed with sandstones which suggests that there was a cyclical alternation between lake environments and alluvial fans. An alluvial fan is a triangular-shaped mass of sediment, deposited when a watercourse passes from a confined channel into a more open area. The layered deposits of fine material with coarser material indicate cyclical fluctuations of water levels within the lake; the finer silts being laid down in deeper, calm environments while the course grained sediments were laid down under shallower, faster-flowing conditions. The grey shales in the sequence contain phosphatic lenses created by the presence of microfossils of simple algae. These microfossils, originally detected by the geological survey nearly a century ago, are an important element of the Torridonian Group flora. They were the first microfossils of this age to be recognised in Britain.

Plant communities

A9 — Fast flowing river and stream, Marginal and inundation, Pond ditch and canal, Sluggish river and stream

Potamogeton natans community

Schoenoplectus lacustris, Juncus bulbosus, Sparganium angustifolium, Sparganium erectum, Sparganium minimum, Alisma plantago-aquatica, Lobelia dortmanna, Equisetum fluviatile, Myriophyllum alterniflorum, Elodea canadensis, Lemna minor, Lemna trisulca, Nymphaea alba, Callitriche platycarpa, Callitriche stagnalis, Littorella uniflora, Potamogeton natans, Ranunculus trichophyllus, Glyceria fluitans, Chara subspinosa

A14 — Fast flowing river and stream

Myriophyllum alterniflorum community

Isolepis fluitans, Juncus bulbosus, Fontinalis antipyretica, Lobelia dortmanna, Equisetum fluviatile, Myriophyllum alterniflorum, Lemna minor, Callitriche stagnalis, Littorella uniflora, Potamogeton filiformis, Potamogeton gramineus, Potamogeton natans, Ranunculus peltatus, Chara spp., Nitella hyalina

A17 — Chalk river and stream, Fast flowing river and stream

Ranunculus penicillatus ssp. pseudofluitans community

Berula erecta, Nasturtium officinale, Elodea canadensis, Lemna minor, Callitriche stagnalis, Veronica beccabunga, Polygonum amphibium, Polygonum hydropiper, Potamogeton crispus, Potamogeton pectinatus, Ranunculus penicillatus ssp. pseudofluitans

A18 — Fast flowing river and stream

Ranunculus fluitans community

Fontinalis antipyretica, Fontinalis squamosa var. curnowii, Myriophyllum alterniflorum, Myriophyllum spicatum, Elodea canadensis, Mentha aquatica, Lemna gibba, Lemna minor, Potamogeton perfoliatus, Ranunculus fluitans, Glyceria fluitans, Phalaris arundinacea