Over millions of years the continents of Earth have moved and changed, until they formed the shapes we recognise today. Mountain-building is a result of the constant movement of plates on the surface of the Earth, driven by heat from Earth’s core.

The process of mountain-building is called an ‘orogeny’. An ‘orogenic belt’ develops when a compressed plate crumples and is uplifted to form one or more mountain ranges.

There are two different histories of mountain formation in Lochaber; on either side of the Great Glen. The rocks to the north of the Great Glen are called the Moine Supergroup. They began as mud and sand deposits in a shallow sea, on the edge of a supercontinent called Rodinia. Mountains formed between 800 and 400 million years ago. Heat and pressure deep in the mountain range caused the minerals in the rocks to recrystallize, a process called ‘metamorphism’. The most common Moine rock is schist, which contains shiny flakes of mica, a mineral.

To the south of the Great Glen, the mountains are built of rocks called the Dalradian Supergroup. They were formed from ocean sediment between 800 and 600 million years ago on the edge of an ancient continent called Laurentia. The Dalradia rocks include white quartz, marble and slate.

When two adjacent sections of Earth’s crust have different geological histories they are called ‘terranes’. The Great Glen fault is a ‘terrane boundary’ between the Northern Highland Terrane and the Grampian Terrane.

Lochaber boasts some of the best geology in the world, with Scotland’s highest mountains and deepest lochs.

The most famous part of Lochaber’s geology is, of course, Ben Nevis!

Did you know that Ben Nevis used to be a massive active volcano?

Our favourite local mountain is 420 million years old. Like almost all of Scotland’s highest mountains, Ben Nevis has a granite core. Granite is very hard and survives better than many other rocks.

What is unique about Ben Nevis is its pile of surface volcanic rocks. These are not lava flows, but evidence of a mighty, explosive eruption.

What we now see is the remains of a volcano that collapsed in on itself. This is called a ‘caldera’; literally, a cauldron.

‘Fossilisation’ is the name of the process whereby a dead animal, insect, fish or plant becomes stone. Most were formed when creature or plant died and was quickly buried by sediment (such as mud, sand or volcanic ash). More sediment, volcanic ash or lava can build up over the buried organism and eventually all the layers harden into rock.

During the Jurassic age, much of Scotland was a large semi-tropical island. Bivalves (a kind of shellfish) inhabited shallow coastal waters and ammonites were plentiful in the open sea. Near Lochaline and Kilchoan, limestone deposits contain numerous fossils. Fossilised oyster shells, known as Gryphaea or ‘devil’s toenails’ (yuk!), are a common find on Lochaber shores, as well as ammonites. These are around 200 million years old.

If you go looking for fossils, please follow the Scottish Fossil Code. Fossils are ‘finite and irreplaceable’ – that means, once they’re gone, they’re gone. New fossil finds add to our record of past life and environments on our planet, but this precious resource is at risk of abuse and damage, and so must be safeguarded to ensure its survival for future generations.

Paleontology also includes the study of dinosaurs. There has been very little evidence of dinosaurs in Scotland, largely because the rocks are much older than the time when the reptiles ruled the Earth. However, north of Lochaber, on the Isle of Skye, there have been significant finds of dinosaur fossils from the Middle Jurassic – which was between 162 million to 175 million years ago.

Palaeontologists say this was a period of time when there was a massive diversification in dinosaurs.