Kokelaar, B P, And Moore, I D. 2006. Glencoe caldera volcano, Scotland. Classical areas of British geology (Keyworth, Nottingham: British Geological Survey.)

An accompanying 1:25,000 map is available for viewing on the BGS Maps Portal

Appendix Key field localities

The following text and map are provided to help the interested geologist locate and examine key features in the field. They are best used in conjunction with the 1:25 000 scale geological map (British Geological Survey, 2005). UK National Grid references all refer to the 100 km square NN. The brief notes regarding access are for general guidance only.

It is stressed that this appendix is not intended as a field guide. All terrain in the Glencoe area is potentially hazardous and all field visits should be planned accordingly. Much of the terrain is very steep and remote. Serious deterioration in weather conditions can occur with surprising rapidity and streams and rivers can quickly become impassable torrents. Some descent routes are not straightforward and can be long and arduous. No listed locality is perfectly safe and visits to those described in the notes as steep, exposed, or involving a scramble should only be undertaken by persons who are experienced and confident in mountain environments, with due regard for prevailing and predicted weather conditions. Some of the listed localities are unsuitable for large parties and potential leaders are advised to check access in advance, bearing in mind the abilities of likely participants.

Many localities are geological Sites of Special Scientific Interest (SSSIs). The use of hammers and sampling without permission from Scottish Natural Heritage is prohibited by law.

Location map of key field localities (Figure 29).

Locality Grid reference Key features Relevant page, figure or plate Notes
1 [NN 153 573] Palaeocanyons in tilted unconformity surface. Conglomerates with boulders over 1 m in diameter include diverse plutonic rocks. Plant remains recovered from siltstone nearby 31–32; 104

(Plate 5)

 Exposures along foot of cliffs
2 [NN 138 563] Leven Schist Formation constitutes local basement beneath volcanic succession 22; 87 Numerous exposures
3 [NN 1399 5598] Unconformity. Reddened Leven Schist Formation cut by irregular erosion surface and overlain by schist-breccia, sandstone and andesite of Basal Andesite Sill-complex 30 Small exposure beside stream (east bank)
4 [NN 1408 5594]–[NN 1402 5591] Peperitic top of basaltic andesite sill. Overlying sandstones show soft-state convolution and small-scale faulting. Basal part of succeeding sill shows lobate form and peperite in fractures 33

(Figure 9)

 Steep access down to exposure at upper plunge-pool
5 [NN 1398 5516] Coarse peperite and autobreccia forming top of andesite sill 33

(Plate 6a)(Plate 6b)

 Extensive exposure
6 [NN 1420 5538] Peperitic top of uppermost sill unconformably overlain by sandstone and then accretionary-lapilli-bearing Kingshouse Tuffs 34; 38; 104

(Plate 7); (Plate 10)

 Access traverse is in exposed position
7 [NN 139 548] Kingshouse Tuffs and Lower Etive Rhyolite steepen and are restricted at overturned scarp of Southwestern Graben Fault 27; 49; 87

(Figure 14a)(Figure 14b)

 View, partly in steep cliff face
8 [NN 142 548] Lava-like ignimbrite of Lower Etive Rhyolite overlain by Upper Three Sisters Ignimbrite, which is eutaxitic and includes mesobreccia 69

(Figure 14); (Figure 21)

(Plate 19a)(Plate 19b)

 Extensive exposures
9 [NN 1428 5455]–[NN 1434 5420] Andesitic Church Door Buttress Breccias bury trace of Southwestern Graben Fault. Overlying Bidean nam Bian andesite has columnar joints more than 150 m tall 73–74; 78; 83

(Figure 14); (Figure 23)

 Steep cliff exposures above scree-lined gully
10 [NN 1475 5497] Columnar jointing of Bidean nam Bian andesite; jointing indicates single cooling unit about 200 m thick. Flow-banded domains with diverse orientations locally define solidified lava blocks that foundered into fluid magma 78–79

(Plate 22a)(Plate 22b)

 Extensive exposures amidst large blocks; steep cliffs to north-east
11 [NN 1546 5632] Palaeocanyon about 15 m deep incised in Basal Andesite Sill-complex along the line of Ossian Fault. Palaeocanyon filled with several metres of coarse heterolithic conglomerate dominated by andesite clasts and overlain by ignimbrite (Kingshouse Tuffs) 27; 104

(Plate 4); (Plate 14)

 Steep access
12 [NN 157 561] Upper Streaky Andesite vent with steeply inclined streaking and local bodies of heterolithic agglomerate and breccia. Adjacent Lower Three Sisters Ignimbrite contains veins of the andesite and evidence of ductile deformation due to reheating 74; 105

(Plate 14); (Plate 20)

 Access from below is difficult.

Exposed position
13 [NN 167 556] Postglacial catastrophic rock-fall deposits 109

(Plate 18)

 Access via footpath
14 [NN 1838 5602]–[NN 1808 5688] Dykes of Etive Swarm intrude Upper Etive Rhyolite (lava-like ignimbrite) and are cut by post-Caledonian monchiquite dyke. Palaeocanyon is floored by pebbly sandstone and intruded by Upper Streaky Andesite. Upper Etive Rhyolite is restricted against Basal Andesite Sill-complex at overturned scarp of the Northeastern Graben Fault 27; 53; 57; 100 Exposures along Allt Lairig Eilde and in the the vicinity of ‘The Study’
15 [NN 2006 5556] Lower Queen’s Cairn Breccias, including megablocks, rest on Queen’s

Cairn Conglomerates that locally occupy steep-sided palaeocanyons cut into Lower Three Sisters Ignimbrite

 64; 66

(Figure 17); (Figure 19); (Figure 20)

 Steep access
16 [NN 1875 5704] Lower Queen’s Cairn Breccias rest on Basal Andesite Sill-complex at degraded scarp of Queen’s Cairn Fault.

Overlying Upper Three Sisters Ignimbrite buries several stratigraphical units that were exposed in the footwall of the Northeastern Graben Fault-zone

 66

(Figure 17); (Figure 20)

 Access steep in places
17 [NN 2082 5742] Monzodiorite fault-intrusion; inner contact is a planar fault surface marked by microbreccias, ultracataclasite and pseudotachylite. Outer contact is generally irregular with fault-rocks preserved locally and with pseudo-tachylite lining veins and blocky joint surfaces. Numerous xenoliths in intrusion, including an 8 m-block of ‘granite’. Fault-intrusion along earlier fault at the summit shows brecciation and hydrothermal alteration, with pseudotachylite in veins and along the inner contact 84; 88–97

(Figure 26)

(Plate 25)(Plate 25); (Plate 26a) (Plate 26b) (Plate 26c)

 Access from top of Devil’s Staircase (path); direct ascent from the main road is farther and more arduous than it looks
18 [NN 2285 5455] Sequence of fluvial conglomerate, sandstone and siltstone rests on irregular unconformity surface; conglomerate shows fracture zones parallel to nearby Northeastern Graben Fault-zone. Plant remains recovered from siltstone. Overlying Kingshouse Breccias are substantially restricted at the scarp of a north-east-trending fault; small fault scarp farther south has scarp-foot talus buried by the breccias 34; 38; 40

(Figure 10)

(Plate 8a)(Plate 8b)

 Beneath and on the south side of the slabs known as the Waterslide
19 [NN 2266 5479] Kingshouse Breccias resting on metamorphic ‘basement’ and succeeded by Kingshouse Tuffs tuff-cone succession, lithic-rich towards base and becoming better bedded, finer grained and with accretionary lapilli-rich layers towards the top 38; 40–43; 46

(Figure 12)

(Plate 11a)(Plate 11b)

 Slabby outcrops steepen upwards to exposed positions
20 [NN 211 540] Extensive Glas Choire sandstones gradually steepen in dip towards the south and south-west, becoming vertical, in response to downsag that accompanied emplacement of the overlying Bidean nam Bian andesites and dacites 76; 79
21 [NN 1644 5431]–[NN 1549 5365] Thick eutaxitic Lower Dalness Ignimbrite is overlain by tuffaceous sandstone and accretionary lapilli-bearing uppermost part of the Coire nan Easan Tuffs. Intrusive andesite sheet forms a topographic outlier and is cut by numerous dykes of the Etive Swarm 81–82 Access is steep in places
22 [NN 1606 5324] Fine-grained Coire nan Easan Tuffs interstratified with thin ignimbrites and succeeded by eutaxitic Upper Dalness Ignimbrite 82
23 [NN 1352 5100] Monzodiorite fault-intrusion with steep contact against volcanotectonic fault, cut by several dykes of Etive Swarm 86

(Figure 25)

 Exposures along river
24 [NN 154 516] Multiple dyke including porphyritic varieties of microdiorite and microgranite (see Bailey, 1960, p.198) 100 Exposure in river bed
25 [NN 204 512]–[NN 198 507] Etive Dyke Swarm constitutes approximately one third of outcrop; dykes include porphyritic varieties of microdiorite, quartz-microdiorite and microgranite 29; 100 Exposures along River Etive and in stream above Alltchaorunn
26 [NN 239 528]–[NN 240 516] Rhyolite dykes in flaggy quartzite ‘basement’. Lacustrine facies Kingshouse Tuffs overlain by Etive rhyolites (lava-like ignimbrites) and eutaxitic Three Sisters ignimbrites. Lowermost parts of Bidean nam Bian Andesite Member show pillow forms with intervening siltstone and peperite, recording shallow intrusion into wet caldera-lake-floor sediments 46; 79

(Figure 11)

(Plate 12a)(Plate 12b); (Plate 16a)(Plate 16b); (Plate 17)

 Scramble up ridge; steep in places
27 [NN 247 521] Rhyolite and rhyolitic tuff with breccias form irregular dykes that mark a zone of discontinuous fractures in the metamorphic ‘basement’ along the North-eastern Graben Fault-zone 64

(Figure 17)

(Plate 17)
28 [NN 244 516]–[NN 241 514] Lower Three Sisters Ignimbrite thickens dramatically across Chasm step-faults where Upper Etive Rhyolite megablocks show downsag-related detachment on underlying Crowberry Ridge Tuffs.

Glas Choire conglomerates in palaeo-canyon include boulders of metamorphic ‘basement’ and granite

 60–61; 75–78

(Figure 18); (Figure 24)

(Plate 17); (Plate 21a)(Plate 21b)(Plate 21c)
29 [NN 2506 5168] Crevasse formed in Northeastern Graben Fault-zone contains megabreccia of metamorphic ‘basement’ with mesobreccia-bearing eutaxitic

Lower Three Sisters Ignimbrite in upper levels; eutaxitic fabric locally steep and parallel to crevasse wall. Lower Etive Rhyolite originally restricted at fault-scarp shows downsag towards south-east

 62; 64

(Figure 17); (Figure 18); 48
30 [NN 2386 5001]–[NN 2388 5076] Clach Leathad hornblende-biotite monzogranite; contacts of pluton with volcanic succession define steep wall and shallow-dipping roof 98–100 Magnificent views
31 [NN 178 477] Meall Odhar monzogranite cuts and alters dykes of Etive Swarm, gives rise to a micromonzogranitic dyke and is cut by late dykes of Etive Swarm 98–100

References