Victorian naturalist Charles Darwin needs little introduction. His seminal work, On the Origins of the Species, published in 1859, fundamentally shaped the theory of evolution.
Having said that, it is perhaps not as generally known that Darwin was, in fact, also an accomplished geologist and that some of his earliest scientific endeavours and achievements dealt with that field. Within this bracket of his career, an even more obscure fact is that some of his early geological observations concerned the 540-million-year-old Sea Point Contact, a complex and dramatic contact between an intrusive granite and a sedimentary rock, which he made during a brief sojourn in Cape Town when he undertook an epic five-year-long exploratory voyage on the HMS Beagle.
According to an autobiographical note, Darwin’s interest in natural history and, more especially, in collecting natural rocks and specimens, developed at a very early age. In fact, he noted that his earliest geological aspiration emerged at the age of just nine, when he experienced a desire to “know something about every pebble in front of the hall door”.
While keenly interested in geology, when Darwin entered the University of Edinburgh in 1825 (at the age of just 16) it was for a medical degree that he enrolled, presumably to follow in the career path of his father and grandfather, who had both been doctors. As part of that degree, Darwin attended various lectures on natural sciences, including a few on geology, which were presented by Robert Jameson, a professor of natural philosophy. Unfortunately, the young student found Jameson’s lectures “incredibly dull”, their sole effect being the “determination never as long as I lived to read a book on geology or in any way to study the science”. But it would seem that Darwin did not enjoy his studies in general at Edinburgh, for he left after two years without having graduated.
Aged 18 when he left university, Darwin contemplated a career in the clergy, but, as he needed a BA degree, he opted to enrol for this degree at Christ’s College, Cambridge. It was during this time that he became associated with two natural science professors at Cambridge, John Stevens Henslow and Adam Sedgewick, whose work and friendship had the effect of restimulating his interest in the field of geology. In particular, it was a field excursion to North Wales in 1831, led by Sedgewick, that laid the foundations of Darwin’s career as a geologist, with the young man producing his first notes and map from observations made during that trip.
Shortly after his return from Wales, Darwin received an invitation from Captain Robert Fitzroy to accompany him as a companion and fellow naturalist on an exploratory voyage aboard the survey barque HMS Beagle. The purpose of this voyage was to primarily conduct a detailed hydrographic survey and improve the nautical maps of South America. It was also intended to collect natural specimens from the distant continent, in addition to gathering geological evidence that could support the theory of the Biblical flood, a global event that was considered to be real by most geologists of the day.
To welcome his companion on board, Fitzroy gave Darwin a copy of Charles Lyell’s recently published and highly popular Principles of Geology, which largely popularised James Hutton’s concept of uniformitarianism. It has often been stated that it was Lyell’s theories that really cemented Darwin’s passion for geology.
Most of Darwin’s epic voyage is beyond the scope of this piece, but suffice to say that, over the course of four years, he visited and made extensive surveys of the Cape Verde Islands, Brazil, Argentina, Falkland Islands, Chile, the Galapagos Islands, Australia and Mauritius before landing in Table Bay on June 1, 1836. The party spent a relatively short time in Cape Town, the stop being meant only as a brief victualling on their long voyage back home to England.
While there, Darwin met and was accompanied on a tour of the most important geological sites around the Cape Peninsula by Scottish surgeon, naturalist and zoologist Andrew Smith, who also happened to be the first superintendent of the South African Museum of Natural History. He was taken to, and made geological and geographical observations of, the road from Simonstown to Cape Town, Table Mountain, Lion’s Head and Signal Hill, the road to Paarl, Paarl Rock, the Drakenstein Mountains, Franschoek and the pass to Houw Hoek, Sir Lowry’s Pass and the Cape Flats.
However, by far the most famous geological observation Darwin made on that trip was that of the Sea Point Contact zone, where a distinct intrusion of molten granite through rocks of the Malmesbury Group is clearly visible. That geological phenomenon is renowned for having assisted in proving that granite is an igneous rock emplaced within older, pre-existing rocks. At a time when the field of geology was still relatively in its infancy, debates concerning the origins of rocks and formations, particularly that relating to phenomena such as the Sea Point Contact, raged among geologists. While many geologists had, and have since, debated the nature of that phenomenon, Darwin’s own contribution to the debate was that “they were interconnected pendant slivers of infolded suprapositional schists that were intruded parallel to their schistosity by thin fingers of granite, and then eroded to reveal apparently detached schist fragments in the granite”.
These observations were recorded for posterity in Darwin’s Geological Observations on the Volcanic Islands, visited during the voyage of the HMS Beagle in 1844.
Such is the noteworthiness of the Sea Point Contact and Darwin’s visit to the Cape and his geological observations of the phenomenon that he is mentioned in a bronze plaque erected by the South African National Monuments Council at Saunder’s Rocks near Sea Point in 1953. Although still there, that plaque has been superseded by another information board, which was erected by the City of Cape Town in December 2010. It describes the significance of the outcrops in three languages – English, Afrikaans and Xhosa – and includes information about Darwin’s visit and a drawing of the Beagle.