View of geology discovery slope, near Brynrefail

Link to Welsh translationView of geology discovery slope, near Brynrefail

If you’ve just scanned the QR codes beside Lôn Las Peris, look across the lake at the steep and largely wooded hillside opposite. That area played a key role in our understanding of how and when the Earth’s landforms were created – the subject of an intense quarrel between two leading geologists.

Adam Sedgwick (1785-1873) and Roderick Impey Murchison (1792-1871) were intellectual soulmates. In the 1820s they explored Scottish geology together. Early the following decade, Murchison studied fossils in South-east Wales and neighbouring areas of England. He defined a period of geological history which he named the Silurian, after a British tribe which inhabited South Wales when the Romans invaded.

Meanwhile, Sedgwick pursued similar studies in Snowdonia. The slopes around Fachwen, which you can see over the water, were particularly interesting to him because they showed clearly how layers of sedimentary rock were formed at different times. Quarries and related infrastructure had recently exposed sections of rock there. Sedgwick also defined a geological time period and named it the Cambrian, the Roman name for Wales.

The two friends jointly presented a scientific paper in 1835 which outlined how the Cambrian and the later Silurian were different periods in history. The two then disagreed over the boundary between the periods. Eventually Murchison even proposed that the Cambrian period was simply the early part of the Silurian. No fossils older than Cambrian were known, and both men may have wanted everlasting fame for identifying the Earth’s first rocks! The men refused to speak to each other for years.

The solution to the dispute came soon after both had died, with the definition of the Ordovician period – after the Cambrian and before the Silurian. The Ordovices were another pre-Roman tribe in Wales.

Sedgwick’s work in North Wales sent ripples further through scientific history because on his summer 1831 exploration he brought along a young scientist named Charles Darwin, whose education in field study with Sedgwick helped him to refine the evolution theory which he and Alfred Russel Wallace developed.

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Footnotes: How old are Welsh hills?

Cambrian period: 542 to 488 million years ago

Ordovician period: 488 to 444 million years ago

Silurian period: 444 to 416 million years ago