Saturday, 13 June 2015

A Geological Wander

There's a section of coast towards the end of Ormsaigbeg which offers a huge range of geological treasures to anyone interested enough to scramble down to it and spend a few hours wandering across the rocks.

Most people who have studied geology will have heard of Ardnamurchan for its Tertiary ring complex, the huge, 60 million year old volcanic structure that built the central part of the peninsula.  There's plenty of evidence of its activities along this coast. In this picture, one of the cone sheets runs left to right. It was later been cut by an unusually sinuous dyke, running straight up the picture.

A volcano has to sit on something, and one of the pleasures of this small area is that one can see and study one of the older rocks that lies beneath the volcano.  It's a limestone of Jurassic age, and in this picture its beds can be seen dipping away towards the sea.

This limestone is crammed with fossils. In this picture, the bullet-shaped creatures to the left are belemnites, a early and extinct relative of the modern-day cuttlefish, while to the right is the characteristic whorl of an ammonite.

Undoubtedly the most spectacular of the fossils in these rocks is this nautilus.  Nautiluses still roam the seas today, mostly in the Pacific.  They're unusual as an animal in that they haven't changed much in some 500 million years, their design being so robust it has taken them through several mass extinctions, including the one that destroyed the ammonites and dinosaurs.

Some of the fossils aren't at all what they appear to be.  The beastie on the left, which looks so like a fish, is more likely to have been formed in some way from a mollusc shell.  The faint impression at top right, however, is clearly recognisable as an ancient ancestor of the scallop.

Further along the coast, more sedimentary rocks are visible in the side of a bay.  Their colour and patterning suggest that they may have been deposited in a dry environment such as a desert, or possibly along an arid coastline at the back of the warm, shallow sea that hosted the ammonites, nautiluses and belemnites.


  1. I can't believe that there are so many old fossils in Kilchoan!


  2. Think they might be 'belemnites '