Anderson, F.W. and Dunham, K.C. 1966. The geology of Northern Skye

The geology of Northern Skye

Explanation of the Portree (80) and parts of the Rubha Hunish (90), Applecross (81) and Gairloch (91) sheets

By F. W. Anderson, D.Sc., F.I.BioL., F.R.S.E. and K. C. Dunham, D.Sc., S.D., M.I.M.M., F.R.S.

Institute of Geological Sciences, Natural Environment Research Council

Memoirs of the Geological Survey of Great Britain, Scotland

Edinburgh: Her Majesty's Stationery Office 1966

Frontispiece (Plate 1) (D3173) A. The Storr from the south; part of the Trotternish lava-scarp (D3172) B. Landslip topography south of Flodigarry Hotel (D3171) C. Staffin Bay from the North

The Institute of Geological Sciences was formed by the incorporation of the Geological Survey of Great Britain and the Museum of Practical Geology with Overseas Geological Surveys and is a constituent body of the Natural Environment Research Council

© Crown Copyright 1966. First published 1966 Second impression 1980. ISBN 0 11 887412 8

Preface

The area described in the present memoir was surveyed on the six-inch to the mile scale by the late J. K. Allan, the late D. Haldane, Mr J. Knox, Mr. T. R. M. Lawrie, Dr. T. Robertson with the late G. V. Wilson as District Geologist between the years 1934–39. Certain marginal areas, partly surveyed in 1894–98 by A. Harker and H.B. Woodward, were re-examined by Messrs. F. W. Anderson, J. Knox and T. R. M. Lawrie. The Jurassic coastal areas were visited by C. B. Wedd in 1912 and in 1913 by G. W. Lee, who made certain modifications in the earlier mapping. During 1936–38 and 1947 Dr. F. W. Anderson made a detailed examination of the Jurassic and Tertiary sediments and remapped some areas. The late Dr. L. F. Spath contributed greatly by identifying all the ammonities and the late Sir Albert Seward and the late W. N. Edwards reported on the Tertiary plants. The remaining fossils have been identified by Dr. F. W. Anderson. The petrographical investigation of the lavas and minor intrusions begun by Dr. K. C. Dunham during his period as Chief Petrographer was continued by him after he resigned to become Professor of Geology at Durham.

The maps have been compiled and seen through the press by Dr. Anderson; the composite one-inch map comprising the Portree (80) Sheet, the Skye portion of the Rubha Hunish (90) Sheet and part of the Applecross (81) and Gairloch (91) sheets was published both in solid and drift editions in 1964. Dr. Anderson has also written the memoir except for chapters 7, 9, and 10, dealing with the petrography, which are the work of Professor Dunham. The memoir has been edited by Dr. G. H. Mitchell.

C. J. Stubblefield Director. Geological Survey Office Exhibition Road, South Kensington, London, S.W.7. 5th May, 1965.

Contents

(References are listed at the end of each chapter)

Preface by the Director

List of illustrations

Explanation of plates

List of six-inch maps

Chapter 1 Introduction

Area and physical features

Summary of geology

Chapter 2 Jurassic

General, Lias and Inferior Oolite

General Account

 Middle Lias

Upper Lias

Inferior Oolite

Chapter 3 Jurassic

Great Estuarine Series

General description

Oil-Shale

White Sandstone

'Estheria' Shales

Concretionary Sandstones

Lower 'Ostrea' Beds

Ostracod Limestones

Mottled Clays

Upper 'Ostrea' Beds

Belemnite Sands

Chapter 4 Jurassic

Oxford Clay to Kimmeridge Clay

Oxford Clay

Corallian

Kimmeridge Clay

Chapter 5 Tertiary sediments

Palagonite Tuffs

Interbasaltic Sediments

Chapter 6 Tertiary lavas

General Account

Beinn Edra Group

Ramascaig Group

Beinn Totaig Group

Bracadale Group

Osdale Group

Magmatic Sources for the Lava Suite

Chapter 7 Petrography of the volcanic rocks

History of research

Palagonite tuffs

Tholeiitic pillow lavas

Main lava series

Hebridean type

Vaternish Hebridean type

Feldspar-phyric olivine-basalt

Mugearite

Big-feldspar mugearite and mugearite-basalt

Trachyte

Chapter 8 Intrusive igneous rocks

Tertiary sills

Dykes

Trachyte

Mugearite

Dolerite

Picritic dolerite

Gabbro and allivalite

Regional dolerite dykes

Multiple intrusions

Age relations of dykes

 Inclined sheets

Vents and agglomerates

Chapter 9 Petrography of the minor intrusions

History of research

Petrography of the sills

Olivine-dolerite

Picrodolerite

Crinanitic and teschenitic dolerites

Pegmatitic dolerite

Chemical composition

Petrography of the dykes

Normal olivine-dolerite and basalt

Crinanitic variants

Picritic dolerites--picrites

Mugearite

Variolite

Leidleite

Trachyte

Feldspar-phyric dolerite and basalt

Allivalite, olivine-eucrite, gabbro

Tholeiite

Porphyritic tholeiites

Chapter 10 Igneous petrology

The initial eruption in North Skye

The Alkaline Olivine-basalt Suite

Allivalitic and Feldspar-phyric Rocks

Summary

Chapter 11 Tectonic history

Pre-Triassic

Post-Triassic—Pre-Tertiary

Tertiary Movements

Chapter 12 Quaternary

Glaciation

Retreat of highland ice

Late-glacial re-advance

Valley glacier retreat stages

Glacial erosion

Glacial deposits

Erratic boulders

Moraines

Sands and gravels

Raised beaches

Landslip

Rockfalls and scree

Diatomite

Alluvium

Blown sand

Olivine sand

Musical sands

Nullipore 'sands'

Chapter 13 Economic geology

Ironstone

Jet

Oil-shale

Lignite

Peat

Diatomite

Road metal

Limestone

Shell sand

Honestone

Water

Appendix List of Geological Survey photographs 203

Index

Illustrations

Text figures

Figure 1. Sketch-map showing distribution of main groups of rocks in Northern Skye

Figure 2. Generalized vertical section of sedimentary and volcanic rocks exposed in Northern Skye

Figure 3. Section in sea-cliff at Fiurnean, 4 miles N.N.E. of Portree

Figure 4. Sections showing the sequence of strata in the Concretionary Sandstones, Lower 'Ostrea' Beds, Ostracod Limestones, Mottled Clays, Upper 'Ostrea' Beds, Oxford Clay, Corallian and Kimmeridge Clay

Figure 5. Section in sea-cliff on north side of Portree Bay

Figure 6. Section in sea-cliff between Upper Tote and Inver Tote

Figure 7. Section in sea-cliff between Drum Dearg and Loch Mealt fall

Figure 8. Map of Jurassic strata in Staffin Bay, coast east of Digg

Figure 9. Map of Jurassic strata in Staffin Bay, coast east of Loch Leum nam Bradh

Figure 10. Map of Jurassic strata in Staffin Bay, coast east of Loch Langaig

Figure 11. Map of Jurassic strata in Staffin Bay, coast south-east of Flodigarry Hotel

Figure 12. Correlation of the Jurassic strata exposed in Staffin Bay

Figure 13. Sketch-map showing the outcrops of the main lava-groups and section showing their mutual relationships

Figure 14. Section showing the behaviour of part of the Tertiary sill-complex at Eist

Figure 15. Modes of a suite of specimens collected at intervals in the central chimney cutting the Meall Tuath upper sill, Rubha Hunish

Figure 16. Plot of compositions of normative feldspars in Hebridean lavas and sills

Figure 17. Variation diagram for the Alkaline Olivine-basalt lavas and minor intrusions

Figure 18. Plots of iron oxide-magnesia ratio and iron oxide-content against silica

Figure 19. Sketch-map showing movement of ice and other glacial features in Skye

Figure 20. Glacial retreat stages in Trottemish, Isle of Skye

Figure 21. The Bracadale—Edinbain late-Glacial lake system at the 550-ft retreat stage

Figure 22. Section of the Quirang Landslip

Figure 23. Section of The Storr Landslip

Plates

(Plate 1) A. The Storr from the south;. part of the Trotternish lava-scarp. Landslipped lavas and Jurassic sediments form the ground to the right of the escarpment. In the foreground a glacially eroded hollow in Jurassic sediments is occupied by the two lochs Fada and Leathan, which supply water for the Bearreraig Hydro-electric Station. (D3173, replaces MN20706); B. Landslip topography south of Flodigarry Hotel. In the foreground slipped masses of Tertiary lava and Jurassic sediments. In the distance the headland of Rubha Garbhaig is of Tertiary dolerite sills in Jurassic sediments.(D3172, replaces MN20704); C. Staffin Bay from the north. On the foreshore are upper Jurassic sediments. In the middle distance Staffin Point (An Corran) is formed by two dolerite sills with Jurassic sediments between them. Behind the storm beach the 25-ft and 50-ft beach flats are well seen and correspond with the rock notches seen in An Corran. (D3171, replaces MN20705) Frontispiece

(Plate 2) A. Bearreraig, six miles north-north-east of Portree. Inferior Oolite sandstone giving rise to waterfall. (C2241) B. Lyndale Point, 100 yd from shore, 1530 yd north-northwest of Lynedale House. Dolerite dyke showing columnar jointing. (C3919)

(Plate 3) A. Bearreraig Bay, 6½ miles north-north-east of Portree. Columnar sill of dolerite overlying Inferior Oolite. (C2244) B. Coast, south of Mealt Waterfall, looking north from Valtos. Great Estuarine Series with intruded sills of dolerite. (C3898)

(Plate 4) The Quirang, looking north-east from Tug road. Escarpment of Tertiary lavas with extensive area of landslipped masses of Tertiary volcanic material. Staffin is on the extreme right. (C3899–3900)

List of Six-inch maps

Geological six-inch maps included wholly or in part in the area covered by the one-inch map of Northern Skye are listed below with initials of the surveyors and dates of survey. The surveyors were J. K. Allan, F. W. Anderson, D. Haldane, J. Knox, T. R. M. Lawrie, T. Robertson and G. V. Wilson.

The maps all belong to the County Series. Maps on the National Grid were not available at the time of preparation. The completed maps are deposited at the Geological Survey Office, 19 Grange Terrace, Edinburgh, 9, where they are available for public reference.

1 N.E. Fladda-chuain D.H. 1934
2 S.W. Rubha Hunish D.H., F.W.A. 1935–36
3 N.E. An t'Iasgair D.H. 1934
3 S.E. Kilmuir D.H., F.W.A. 1934–36
4 N.W. Kilmaluag D.H., F.W.A. 1935–36
4 N.E. Bagh nan Gunnaichean D.H., F.W.A. 1934–36
4 S.W. Heribusta D.H., F.W.A. 1934–36
4 S.E. Flodigarry D.H., F.W.A. 1934–36
5 N.W. Vaternish Point D.H. 1935
5 S.W. Unish D.H. 1935
5 S.E. Eilean Iosal D.H. 1935
6 N.E. Balgown D.H., F.W.A. 1935–36
6 S.W. Sgeir a'Chapuill D.H. 1935
6 S.E. Totscore LK., F.W.A. 1934–36
7 N.W. Suidh' a'Mhinn D.H. 1934
7 N.B. Stenscholl D.H., F.W.A. 1934–36
7 S.W. Ben Gorm J.K. 1934
7 S.E. Loch Dubhar-Sgoth J.K. 1934
8 N.W. Rubha Garbhaig D.H., F.W.A. 1934–36
8 S.W. Loch Mealt J.K., F.W.A. 1934–36
9 N.W. Trumpan D.H., F.W.A. 1935–37
9 N.E. Geary D.H. 1935
9 S.W. Ardmore Point D.H. 1935
9 S.E. Score Horan D.H. 1935
10 N.W. South Ascrib D.H. 1935
10 N.E. Earlish J.K. 1934–35
10 S.W. Creagan Glasa D.H. 1935
10 S.E. Lyndale Point D.H., J.K. 035–36
11 N.W. Beinn Fhuar J.K. 1934–35
11 N.E. Beinn Edra J.K. 1934–35
11 S.E. Creag a'Lain J.K. 1935–37
12 N.W. Lealt J.K., F.W.A. 1934–37
12 S.W. Creag Langall J.K., F.W.A. 1934–37
14 N.E. Dunvegan Head D.H. 1939
14 S.E. Boreraig J.K.A., D.H. 1938–39
15 N.W. Lovaig Bay D.H. 1935–36
15 N.E. Loch Bay D.H., F.W.A. 1935–37
15 S.W. Beinn Mhic Uilleim D.H. 1936–39
15 S.E. Bay River D.H. 1936
16 N.W. Greshornish D.H. 1935–36
16 N.E. Kildonan D.H., J.K 1936–38
16 S.E. Flashader D.H., J.K. 1938–39
17 N.W. Kingsburgh J.K. 1936
17 N.E. Hartaval J.K. 1936
17 S.W. Eyre J.K., G.V.W., 1936–37
17 S.E. Glenhaultin J.K., G.V.W. 1936–37
18 N.W. The Storr J.K., F.W.A. 1935–37
18 S.W. Loch Leathan F.W.A.., G.V.W. 1935–37
20 N.W. Oisgill Bay J.K.A., F.W.A. 1938
20 N.E. Holmisdal J.K.A. 1938
20 S.W. Eist J.K.A., F.W.A. 1938
20 S.E. Beinn nan Corrafidheag J.K.A. 1938
21 N.W. Colbost J.K.A., D.H. 1935–36
21 N.E. Dunvegan J.K.A., D.H. 1935–36
21 S.W. Skinidin J.K.A., D.H. 1935, 1938
21 S.E. Kilmuir J.K.A., D.H. 1935–37
22 N.W. Strone Geers D.H. 1936
22 N.E. Ben Uigshader D.H., J.K. 1938–39
22 S.E. Loch Ravag D.H., J.K. 1937–38
23 N.W. Tote J.K., G.V.W. 1935, 1938
23 N.E. Borve G.V.W. 1935–36
23 S.W. Beinn a'Ghlinne Bhig J.K., G.V.W. 1935, 1938
23 S.E. Glengrasco and N.W. Portree G.V.W. 1935
24 N.W. Loch Fada and Lon nam Breac F.W.A., G.V.W. 1935–36, 1939
24 S.W. Torvaig and N.W. Portree F.W.A., T.R.M.L., G.V.W. 1935–36, 1939
26 N.E. Ramasaig J.K.A., D.H. 1938
26 S.E. Lorgill Bay D.H. 1938
27 N.W. Healaval Bheag D.H. 1938
27 N.E. Orbost J.K.A., D.H. 1935, 1937–38
27 S.W. Glen Ollisdal D.H. 1938
27 S.E. Harlosh Point D.H. 1937–38
28 N.W. Loch Caroy D.H., T.R. 1935, 1937
28 N.E. Ben Scudaig D.H., J.K., T.R. 1935, 1937–38
28 S.W. Colbost D.H., T.R. 1935, 1937
28 S.E. Bracadale T.R. 1935
29 N.W. Am Maol J.K., G.V.W. 1935–37, 1939
29 N.E. S.W. Portree and Beinn na Greine J.K., G.V.W. 1935–37
29 S.W. Loch Duagrich J.K., T.R. 1935, 1937, 1939
29 S.E. Mugeary J.K., G.V.W. 1935, 1937
30 N.W. Camas Ban and S.E. Portree T.R.M.L., G.V.W., F.W.A. 1936, 1939
30 S.W. Creag a'Chait T.R.M.L., G.V.W., F.W.A. 1935, 1939
32A Mi-bogha Mor D.H. 1937
32 N.W. Flossnan D.H. 1937–38
32 N.E. Idrigill Point D.H. 1938
33 N.W. Oronsay and Wiay D.H., T.R.M.L. 1935, 1937, 1939
33 N.E. Sumardale T.R.M.L., T.R. 1935, 1939
34 N.W. Glen Vidigill J.K. 1939
34 N.E. Meall an Fhuarain J.K., T.R.M.L. 1939
35 N.W. Beinn nan Capull T.R.M.L., F.W.A. 1938–39
35 N.E. Dunan an Aisilidh T.R.M.L., F.W.A. 1938–39