Igneous Intrusions

The recent cold, dry weather, and the dying-back of the bracken, has made for good walking. These super photographs, taken by Julie Allcock, show geological features on the foreshore between Pier Road and the sea.

The features in the immediate and middle foreground are igneous intrusions, probably of basalt or dolerite. They formed some 55 million years ago when magma from the great Ardnamurchan volcanoes punched upwards into the crust causing cracks to form, into which the magma intruded in sheets and, later, cooled. Since these intrusions are harder than the surrounding rock, they have been worn away more slowly by the ice sheets, rivers and the seas which have worked this land in more recent millennia.

This picture looks across Kilchoan Bay to the hill called Maol Buidhe and the cliffs of Sron Bheag. The large feature on the right is also an intrusion, though its form is less clear. While the intrusions can be in sheets, as in the first picture, they can also form bulbous masses of every shape - depending on the way the cracks developed and on the pressure environment at the time of intrusion.

The area around the Calmac Pier is a geological nightmare, a criss-crossing of original Jurassic sediments and multiple igneous intrusions - exactly the sort of mapping exercise a university lecturer gives to a unliked geology student.