Darwin had originally been introduced to the science of geology during his abortive tenure as a medical student at the University of Edinburgh, though he became actively interested in the subject only as he was completing his degree at Cambridge. Under the influence of the professor of botany (and former professor of mineralogy) John Stevens Henslow, Darwin became fascinated by the thought of travelling to the tropics in emulation of Alexander von Humboldt. Although Humboldt wrote with authority on subjects from botany to political economy, his background was in mineralogy and he had worked as a mining engineer. Inspired by Humboldt’s example, Darwin apprenticed himself to the Cambridge professor of geology, Adam Sedgwick, who had invited the young man to join him on an extended field trip to study the stratigraphy of North Wales. A letter written beforehand to Henslow illustrates Darwin’s unbridled enthusiasm both for the practical work of the geologist and for the invention of geological hypotheses. Sedgwick gave this enthusiasm direction and discipline and inducted Darwin as an interested participant in geological research, which the young man declared ‘I would not give up for any consideration.’
Sedgwick met up with his protégé at the Darwin family home in Shrewsbury in early August 1831 and together they travelled to the Welsh town of Llangollen. Their geological excursion took them west-north-west toward Bangor between 5 and 11 August. Although field notes by both Darwin and Sedgwick have survived, the exact sequence of their movements remains uncertain and is a topic of active research by historians. On 12 August, Darwin may have accompanied Sedgwick to the island of Anglesey, where Henslow had done geological work. At some point Darwin and Sedgwick separated and the younger man traversed back inland by himself, visiting the cliff-encircled lake of Cwm Idwal on his way to meet friends in Barmouth.
Darwin returned to Shrewsbury from Wales on 29 August 1831. He had scarcely put down his geological hammer when he learned that the endorsement of his Cambridge mentors had earned him an invitation to join Robert FitzRoy for a surveying expedition to South America aboard H.M.S. Beagle.
Barrett, Paul. 1974. The Sedgwick-Darwin geological tour of North Wales. Proceedings of the American Philosophical Society 118: 146-64.
Lucas, Peter. 2002. ‘A most glorious country’: Charles Darwin and North Wales, especially his 1831 geological tour. Archives of Natural History 29: 1-26.
Roberts, Michael. 2001. Just before the Beagle: Charles Darwin’s geological fieldwork in Wales, summer 1831. Endeavour 25 (2001): 33-7.
The Sedgwick Museum at Cambridge has a permanent exhibition on Darwin the Geologist. Photographs and further information are available here.