WEGA in the North West Highlands Geopark

Day 1 - Sunday 28th April 2019

We set off on our first day with the purpose of familiarising ourselves with the basics of the geology of the area. Our major stops were at Knockan Crag and Kylesku with a few other stops along the way.

Our route can be seen on the map below. A selection of the my photographs are used below. You can see all of them HERE.

Our first major stop was at Knockan Crag where the amazing geology of Assynt is most clearly displayed. The essential concept displayed in the area is that older rocks have been thrust westwards over younger rocks.

For geologists in the latter part of the 19th century, this was inconceivable. The pictures below illustrate the Assynt succession. Torridonian (very old) sits unconformably on Lewisian (extremely old) and the Cambrian (and Ordovician) rocks (quite old) rest unconformably on the Torridonian. But above the Cambrian (and Ordovician) is the very old Moine. The absolute ages are given on the right.

It was here that the reality of thrust faulting was recognised and the modern understanding of mountain building began.

A good introduction to, what was called “The Highland Controversy” is a book of the same name by David R. Oldroyd. Published by the University of Chicago Press in 1990.
ISBN 0-226-62634-2

Available (at a price!) from AMAZON and presumably other booksellers.

The absolute ages of the rocks are:

  • Lewisian – older than 2,400Ma
  • Torridonian – 1,000Ma
  • Cambrian – Ordovician – 540 – 470Ma
  • Moine – 900Ma
Knockan Crags geology demonstrated in a wall.
The geology wall annotated.

At Knockan we can see one of the thrust faults – the Moine Thrust. There are several more in the zone of thrusting

Moine Schist overlying Durness Limestone. The Moine Thrust between the two

Peach and Horne are the best known of the geologists who elucidated the complex geology of Assynt and they are memorialised at Knockan Crag by two talking statues!

Peach and Horne discuss their legacy

Besides the geology, there is much else to see at the Crag – art installations and the surrounding scenery.

Art installation using local rock carried (thrust?) over the landscape and echoing the mountainous skyline.
Stac Pollaigh

We drove to the banks of Loch Assynt where we looked at the Lewisian / Torridonian unconformity. It is obvious that the Torridonian was laid down on an undulating surface of Lewisian.

Dark Torridonian enveloping a hill of lighter coloured Lewisian. Reflected in the still waters of Loch Assynt

It was then onwards to the Geoparks “Rock Stop Shop” at Kylesku where we looked at, for geologists, the best view in Britain! We also had good coffee and brownies!

The view is of the Ben More Thrust bringing Lewisian over Cambrian Basal Quartzite and Pipe Rock which is unconformably lying on Lewisian. A Cambrian filling to a Lewisian sandwich!

Other views are available at Kylesku

Panorama from the "Rock Stop Shop"
The Stack of Glencoul
Quinag from Kylesku

On leaving Kylesku we drove back almost to Ullapool but, before finishing for the day, entered Morefield Quarry to look at another thrust – this time the Ullapool Thrust. This brings the Ullapool Gneiss (part of the Lewisian) over the Durness Limestone.

The Ullapool Gneiss overlying the Durness Limestone.

After that it was back to Ullapool and prepare for the next day.