“Extracts were read of letters from C. Darwin Esq. of Christ’s College containing accounts of the Geology of certain parts of the Andes and S. America. Observations by Prof. Sedgwick and Henslow.”

They were significant in promoting Darwin’s reputation as a geologist almost a year before the Beagle returned to England, and influenced his father’s decision to support his career as a naturalist.

However, from the outset Darwin was a naturalist in a more general sense and I think it’s not quite right to say that he was mainly a geologist on the day he stepped foot on The Beagle. To quickly review the sporadic development of his interest in geology, after collecting pebbles as a child he went to Edinburgh University and heard both sides of the current debate between Huttonian and Wernerian geology. His recollection was that he “attended Jameson’s lectures on Geology and Zoology, but they were incredibly dull. The sole effect they produced on me was the determination never as long as I lived to read a book on Geology or in any way to study the science.”

His interests in natural history were focussed on marine invertebrates, beetle collecting and then botany with Henslow, as well as a passion for bird shooting. It was only in 1831 during last terms at Cambridge that Darwin read Humboldt’s travels, and became determined to visit Teneriffe. Henslow, who himself had some background in geology, persuaded Darwin to study the subject. Darwin joined Adam Sedgwick’s geology course, then travelled with him in the summer for a fortnight, in order to map strata in Wales.
Darwin returned home from this trip on 29 August to find Henslow’s letter about captain FitzRoy’s offer of a place for a naturalist on the Beagle, “qualified for collecting, observing, & noting any thing worthy to be noted in Natural History”, more as a gentleman companion than a mere collector. Don’t think anything was recorded of it at this time, but in 1839 when writing up accounts of both voyages, FitzRoy recalled examining a rock sample with “regret that no person in the vessel was skilled in mineralogy, or at all acquainted with geology”, and “inwardly resolving, that if ever I left England again on a similar expedition, I would endeavour to carry out a person qualified to examine the land.”
At some early point, Fitzroy gave Darwin the first volume of Lyell’s ‘Principles of Geology’, and on their first stop ashore at St. Jago Darwin put this to good use, starting work geologising on 17 January 1832. From his autobiography, “It then first dawned on me that I might perhaps write a book on the geology of the various countries visited, and this made me thrill with delight.”

Regardless, dolerite forms some really interesting-looking formations, my mind got blown on a recent visit to Cape Raoul.

Also, dolerite is a rock, not a mineral. It’s composition is similar to plutonic gabbro , and volcanic basalt. Here is more information; http://www.scran.ac.uk/packs/exhibitions/learning_materials/webs/43/dolerite.htm

Anyway, knowing good ol’ Chuck was here before me has been a wonderful thought to keep in the back of my mind, and the combination of stunning geology and intriguing biology here makes me think that Charles wasn’t too much in the habit of dividing his attention strictly between the two realms. If you spot a new-to-science insect sitting on a rocky outcrop of Dolerite, a mineral that dominates Tasmania (and almost nowhere else) and is on the surface as a result of some very impressive volcanic activity, do you reach for your killing jar or for your rock hammer? Both, of course!