When one thinks of the 'naturalist' Charles Darwin, it is his contribution to our understanding of how living creatures evolved that casts anything else he might have done into the shadows.

But Darwin's skills were certainly not limited to theorising on the survival of the fittest nor were his eyes fixed only on living creatures as he embarked on his epic voyage on the HMS Beagle in 1831. He was, in fact, a skilled and influential geologist whose work continues to resonate in the field. He was, for instance, the first to make a geological cross-section of the Andes mountains in South America. He also made important observations on both the development of volcanoes and in explaining the occurrence of coral atolls.

Darwin was born just over 200 years ago on February 12 1809 and lived as a child in Shrewsbury on the eastern border of North Wales. He went to Edinburgh University at the age of 16 to become a medical doctor like his father and grandfather before him. While there, he attended lectures in geology, palaeontology, crystallography and mineralogy.

Unfortunately, one geology professor, Robert Jameson, was so tedious and dull that Darwin vowed never again to read a book on the subject. Not enjoying his medical studies, he dropped out of Edinburgh University in 1827, at the age of 18. He then went to Cambridge University to study for a BA. His mentor was Professor John Henslow, a mineralogist and botanist, who often invited Darwin to his home to meet famous scientists and often went on long walks with him, so much so that other professors called Darwin, 'the man who walks with Henslow'.

Henslow persuaded Darwin that he simply had to have a foundation in geology and offered to train him privately. Darwin then bought a clinometer and practiced using it by tipping the tables in his room, back home in Shrewsbury to many different angles, so that he could write to Henslow, 'I will venture to say I have measured them as accurately as any Geologist could do'.

During the summer of 1831, Henslow asked Adam Sedgwick, then in his heyday as a professor of geology at Cambridge, to take Darwin with him to North Wales., despite Darwin never having attended Sedgwick's lectures. In early August of that year, Sedgwick and Darwin rode on horseback into the Welsh hills, where Sedgwick trained Darwin to become a field geologist. He later wrote to Henslow from Rio de Janeiro in Brazil in May, 1832 “…(Sedgwick) does not know how much I am indebted to him for the Welch (sic) expedition, - it has given me an interest in geology, which I would not give up for any consideration…Tell him that I have never ceased being thankful for that short tour in Wales”.

At about the same time, the first volume of the first edition of Charles Lyell's famous book Principles of Geology was published. This became Darwin's geological Bible.

On returning home, Darwin received a very important letter from the Admiralty, via Henslow, inviting him to participate in a 2-year circumnavigation of the world, at his own expense, aboard the H.M.S. Beagle, as a gentleman companion to the hydrographer, Captain Robert Fitzroy. The invitation was from Francis Beaufort, the Hydrographer of the Admiralty. Darwin accepted the invitation and the voyage began on December 7 1831 in Plymouth and lasted, in the end, for nearly 5 years. The journey, which came to an end on October 2 1836, included an 18-day stopover in Simon's Town.

The epic journey on the HMS Beagle had some extraordinary geological highlights for Darwin including the discovery of a giant extinct sloth in soft rock off the coast of Chile and personal experiences of both a massive earthquake and an erupting volcano. He was not only the first scientist to make a geological cross-section of the Andes, he also found a forest of silicified trees, since dated by South American geologists as Triassic, still known as the Darwin Forest. The forest is still marked with an appropriate plaque, erected in 1909, honouring Carlos Darwin, 100 years after his birth.

Darwin had longed to see a coral reef and, around the Polynesian island of Moorea, he saw surf breaking on a fringing reef and a lagoon with transparent water surrounding a volcanic island. Darwin had studied Lyell's views on corals, the living polyps of which can only live in the warm, transparent, illuminated surface waters of the ocean. In Lyell's view their circular shape meant that they grew around the rims of submerged volcanic craters. In contrast, Darwin modified his mentor's ideas and concluded that the atolls originally were fringing reefs around a since-sunken volcanic island.

After leaving the Cocos Islands, off Indonesia, the Beagle crossed the Indian Ocean to reach Mauritius off the east coast of Madagascar on April 24 1836. Being on the homeward leg of the voyage, Darwin was starting to think of his post-Beagle future. He wrote from Mauritius to his sister, Caroline: “I am in high spirits about my geology, - and even aspire to the hope that my observations will be considered of some utility by real geologists”.

Two centuries later, real geologists consider Darwin's contribution to their field to have been very significant indeed.

Dr John Rogers is based at the Department of Geological Sciences at the University of Cape Town. This article is based on a recent address commemorating the 200th anniversary of Darwin's birth.