Darwin’s Boulders, Cwm Idwal


Darwin’s Boulders, Cwm Idwal. Photo © Warren Kovach

6 October 2014

Every year I look forward to returning to Cwm Idwal – it is that kind of place.   Although I have lost count of how many times I have been there, each visit is different and memorable.  You are guaranteed to see something new or have your eyes opened to the environmental processes in operation.

Today I took part in the field studies module for 3rd year freshwater ecosystem students at Bangor University.   We thought our luck had run out because after one of the driest Septembers on record, it was raining.   As we paused on the path to look at the glacial features of the landscape, a complete rainbow formed over the Nant Ffrancon valley.

Charles Darwin also has a record of returning from and to Cwm Idwal and seeing features with greater insight.

At the start of the fieldtrip I told the students that in 1831 when Darwin returned from his first visit to Cwm Idwal, he found a letter inviting him to be an unpaid naturalist with Captain Fitzroy on the voyage of The Beagle.   Under pressure from his father he turned it down but his uncle mediated and gained consent.   It seems Darwin had been extravagant, living beyond his means as a student at Cambridge and to placate his father, he said “that I should be deuced clever to spend more than my allowance whilst on board the Beagle.”   I am pretty sure this argument would not work as a justification for a gap year today but Darwin immediately set off to meet Fitzroy in London.   The rest is history.

During the voyage of The Beagle Darwin developed his understanding of geological processes.  In particular, he became a convert to the new and controversial hypothesis that parts of the earth were once covered by extensive ice sheets that had subsequently retreated.

In 1842 Darwin returned to Cwm Idwal with his geology teacher Sedgwick and made the landmark interpretation of the glacial history of the landscape.   In particular, he referred to a cluster of four large boulders set back from the lakeshore near the outflow.  He proposed that they had been transported to this point by a glacier.  One of the boulders is clearly split into two, and Darwin imagined it falling through a crevasse in the glacier.  You can still do this at Cwm Idwal and no doubt some of readers of this blog will remember this spot as welcome shelter from the wind or rain.

Later in life Darwin asked himself how could he have been so blind on his first visit?

By the time we had navigated our way around the lake today and across the numerous streams in full spate, the sun was shining on the waterfalls above our heads.  The lake surface glistened.  It was memorable to stand beside Darwin’s boulders and listen to the students debate how high the ice would have been over their heads if they could have stood at this spot during the Last Ice Age.


Bangor University students at Cwm Idwal, 6 October 2014.

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