In the footsteps of Mike Coward

NW Scotland Field Excursion May 2004 that the preceded “Continental Tectonics – the Mike Coward Meeting”

Itinerary led by Rod Graham (Outer Isles) and Rob Butler (Moine Thrust Belt).

The trip was designed to visit many parts of the NW Highlands and Islands that were dear to the heart of Mike Coward. They include key sites for his PhD researches in the Lewisian geology of the Uists together with his highly influential work of the late 1970s and early 80s in the Moine Thrust Belt. This report on the field trip has been prepared by Rob Butler. There are lots of additional materials available via links below.


Rob Butler, Dave Carter, Martin Casey, Giulio Casini, Dave Coller, Rod Graham, Gordon Koll. Rick Law, Stefano Mazzoli, Rick Sibson, Roberta Somma, Simon Stewart, Dan Tatham, James Trude, Stefano Vitale, John Wheeler

The programme


After meeting most of the team in Inverness, in pouring rain we drove west to Torridon, using a break in the weather to introduce Highland newcomers to the main units. We could just about make out imbricates on Beinn Eighe through the clouds. Some of the Lewisian geology was rather clearer around Shieldaig, accessed with a quick hack over the bogs. A fast drive via the bridge got us to Sligachan on Skye and a rendezvous with Dave, and Gordon.


The early ferry from Uig got us to North Uist by late morning. Excellent weather meant heading straight down to South Uist, checking out pseudotachylites on the promontory of Aird a’Mhuile. With Simon Stewart joining the team, flying into Benbecula, we all met on the shore of Loch Aineort for an afternoon stroll into the Eastern Gneisses, crossing the Outer Isles Fault Zone on Ben na Hoe.


A coastal walk, NW North Uist (with some scrambling over coastal outcrops), to look at the structural geometry in a part of the islands where Laxfordian deformation is significant. This is one of the most dramatic sections of rocks deformed under mid-lower crustal conditions anywhere around. A central theme was the role of simple shear in the deformation – appropriately as the transect includes the classic examples of shear zones described by Ramsay and Graham (1969) at Castel Odhair. A stunning day out.


After checking out of the hotel we checked out those classic Mike locations of Garry a Siar and Ardivachar where Scourian agmatites are cut by Scourie dykes – sites of low Laxfordian strain. These are great sites for examining heterogeneous strain, and the deformation of Scourie dykes. Before catching the afternoon ferry back to Uig we dashed over Udal to check out similar things on the North Uist coast. A few couldn’t quite leave the islands without taking in a final bunch of pseudotachylites just outside Lochmaddy,


Despite the heavy driving around to Ullapool the previous evening we left early for the long haul north. First stop was Durness – a chance to check out one of the best (and least known!) exposures of the Moine Thrust together with the normal faults that drop it down into the Sango bay sections. Then it was off to the hallowed ground of Ben Arnaboll, its thrust and the underlying imbricates. Unfortunately the rather grotty weather made it difficult to trace the thrust systems out over the hill but at least we got views over that classic MPC ground of Heilam. Then, on the way back, we took in the dramatic road sections at Laxford Brae. This inspired more Lewisian deformation discussions (just don’t mention those flanking folds!) that saw us all the way back to Ullapool.


An early start from Ullapool saw the team at Kylesku for 9 am, ready to catch the Statesman up Loch Glencoul. After landing at the head of the loch, the team hacked up the new eyesore of a track up Glen Coul and then on to the Stack of Glencoul. Rick Law led a discussion on the mylonites and toasted John Christie, who died a few weeks before the trip. We all debated the role of extensional flow and explored Mike’s surge zone model for northern Assynt . On the way back there were vigorous discussions of recent reinterpretations of thrust geometry around the head of Loch Glencoul before the Statesman took us back to Kylesku, a swift beer at the hotel and a return to Ullapool.


Early leavers waited for their taxi to Inverness or longer drive south while the rest of the team headed to southern Assynt to explore Mike’s interpretations of low angle normal faulting, imbrication, surges and the “not-Moine” thrust at Knockan. Great weather, excellent views over Assynt and a quick lunch back in Ullapool were an ideal end for the trip. A quick transfer to Inverness got everyone onto their flights to London and the main meeting.

Thanks to Martin for driving the minibus, and to Jayne Harnett in RDR for organising all the bookings.