A9 Road Cuttings and River Garry Gorge
Geological Conservation Review site | GCR #2692 | Structural and Metamorphic Geology | Dalradian
Scotland's geosites are chosen because of their local, national or international importance. Take only photos, leave only footprints: avoid causing any damage to this site. You can walk almost anywhere in Scotland without the need to ask permission or keep to paths, but you have a responsibility to care for your own safety, to respect people's privacy and peace of mind and to cause no damage.
This site is a Site of Special Scientific Interest (SSSI). It is an offence to intentionally or recklessly damage the protected natural features of a SSSI, and this includes unauthorised sample collection.
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Summary
The Glen Garry localities form an almost continuous section through Grampian Group rocks in the central Highlands. This area is an exceptional example of Dalradian polyphase folding on a large scale. The particularly clean exposures enable the recognition of the major structural elements, using sedimentary structures and geometry of minor folds.
This composite site includes ten sections from Struan 14km NW towards the Pass of Drumochter, including seven road cuttings along the A9 and three sections in the River Garry. They expose Dalradian metasediments (Grampian Group) displaying complex small and medium scale structures.
From NW to SE, using the site names from the GCR description:
The Stalcair Cut (1), the Wade Stone Cut (2) and adjacent River Garry (3) display part of a large upfold, the Creag a’ Mhadaidh Antiform. Original sedimentary structures in metasandstones indicate that the rocks are upside-down, being on the inverted limb of the Tay Nappe. Folds and other structures of several generations are present. The Edendon Cut (4) and Dalnacardoch Cut (5) display complex structures of up to four generations as well as faults and shear zones. The Allt Crom Cut (6) has three-dimensional exposure of a major antiformal fold. The Black Tank Cut (7) shows a tight antiform with mineralised faults and joint planes. At the Clunes gorge and road cut (8,9) the Clunes Antiform can be identified from detailed study of small-scale structures. Microgranite and microdiorite dykes and sills up to 13m wide cut the metasediments at sites 7 to 9. The river Garry at Struan (10) has excellent exposures of inverted Struan Flags of the Grampian Group. They show F2 folds and well-preserved sedimentary structures including cross-bedding, channels, ripples and sedimentary dykes.
Site information
Access
The Stalcair Cut, Wade Stone Cut, Edendon Cut and Dalnacardoch Cut are on the southbound carriageway; if approaching from the south, there is room to turn round at Dalnaspidal. From the start of the dual carriageway at Dalnaspidal, the Stalcair Cut is at the third layby (no 71), the Wade Stone cut at the fourth (no 70), and the Edendon Cut at the fifth (no 68). The Dalnacardoch Cut is accessed from an un-numbered layby directly east of the Trinafour/Dalnacardoch crossroads. The Allt Crom Cut starts about 500m NW of layby 61 (southbound; this the one that involves the most road verge walking) and the Black Tank Cut is at layby 60, northbound. The Clunes Cut is served by laybys 59 (southbound) and 58 (northbound) and it is possible to get down to the River Garry here via a very steep path. For the river Garry at Struan, the best parking is on the B8079 in Calvine outside the old garage or directly across the road from it (NN80456577). A footpath signposted Old Struan runs from the B847 (Kinloch Rannoch road) bridge along the south side of the river.
Further information
Treagus, J. 2009. The Dalradian of Scotland. Geologists' Association Guide no. 67, 202pp. Excursion Q is Glen Garry.
Safety notes
The A9 is a busy trunk road and the rock cuttings extend up to 200m beyond the laybys. The verges are wide enough to walk along; high-visibility jackets are recommended. Great care required if crossing the road; a quiet Sunday morning is the best time.
Carol Pudsey
Aug. 26, 2024
Stalcair Cut: small-scale open F2 folds.
Carol Pudsey
Aug. 26, 2024
Stalcair Cut: cross bedding indicates younging to the right (south). A combination of lichen growth and weathering means the sedimentary structures can no longer be described as superb.
Carol Pudsey
Aug. 26, 2024
Wade Stone Cut: early quartz veins are folded and cut by later, undeformed veins.
Carol Pudsey
Aug. 26, 2024
Wade Stone cut: the steep limb of the Garry synform.
Carol Pudsey
Aug. 26, 2024
In the Edendon Cut open F2 folds affect quartz veins.
Carol Pudsey
Aug. 26, 2024
The "Dalnacardoch Banded Zone" in the Dalnacardoch Cut. An apparently regular series of flaggy psammites includes isoclinal folds.
Carol Pudsey
Sept. 9, 2013
The rounded hinge of the Bohespic Antiform, Allt Crom Cut. On the right of the photo the psammite beds dip E at 20° and are inverted. On the left they are near vertical and farther west they dip steeply ENE and are the right way up (see photo below).
Carol Pudsey
Sept. 9, 2013
Low angle cross bedding in psammite, west end of Clunes Cut, indicating right way up.
Carol Pudsey
July 15, 2022
Meso-scale NW-verging folds, Clunes Cut. This illustrates the deterioration in exposure quality between 2008 and 2022. From Google Streetview; images © 2024 Google.
Carol Pudsey
Sept. 9, 2013
Vertical microgranite dyke cutting well-bedded psammites, Clunes Cut. Scale: the crash barrier is 1.1m high.
Carol Pudsey
Sept. 2, 2024
Black Tank Cut: a thick quartz-feldspar porphyry sill intruded into flaggy psammites. The sill is displaced by later faulting.
Carol Pudsey
Sept. 2, 2024
River Garry at Struan: psammites (Struan Flags) on gentle limb of F2 fold.
Carol Pudsey
Sept. 1, 2024
River Garry at Struan: psammites on steep limb of F2 fold, with scour structure indicating younging to right (downstream).