Darwin discoveries at Cwm Idwal

With its wildly jagged, wind-battered pinnacles of rock, forged by volcanic fire and shaped by ice, Cwm Idwal is an atmospheric place to be.

Hidden clues to a secret past

Once upon a time, the rocks that form the natural amphitheatre around the mountain lake were under the sea.

Around 500 million years ago they were thrust upwards in a massive subterranean upheaval that saw the creation of all of Snowdonia’s mountains. A range that once rivalled the Himalayas has seen its peaks scoured back by wind and weather to the size we see today.

Charles Darwin investigates

For centuries the secret of Cwm Idwal's birth was just that - a secret. But when Charles Darwin arrived here in 1831 to investigate what would become his world famous but controversial 'On the Origin of Species' publication, he saw the first clues to the formation of Cwm Idwal.

He noticed that the scattered rocks and boulders held tiny fossils of sea creatures and oceanic plant life, perfectly illustrating their previous incarnation as the rocky floor of the Iapetus Ocean.

Darwin’s second discovery

So important were these findings that Darwin and his fellow geologist Adam Sedgwick failed to spot even bigger clues to the next significant chapter in the valley’s history.

It was ten years later that Darwin returned and realised that the landscape had been carved by gigantic glaciers. These rivers of ice had left behind a valley where the evidence is etched into every rock.

Cwm Idwal is the epitome of a glaciated valley and draws thousands every year to study its facinating geology.

In 1954 Cwm Idwal was designated as a National Nature Reserve, the first in Wales.


Discover more about Darwin’s discoveries

Take a look at this short documentary and learn more about the geological and geomorphic processes that created this dramatic and beautiful landscape.