This latter substance, where it is best characterised, is of a yellowish-brown colour, translucent, and with a lustre somewhat resembling resin it is brittle, with an angular, rough, and very irregular fracture, sometimes, however, being slightly granular, and even obscurely crystalline: it can readily be scratched with a knife, yet some points are hard enough just to mark common glass it fuses with ease into a blackish-green glass. Towards the eastern end of this island there occur two craters composed of two kinds of tuff one kind being friable, like slightly consolidated ashes and the other compact, and of a different nature from anything which I have met with described. CRATERS COMPOSED OF A SINGULAR KIND OF TUFF. I can't think of a better place to begin our explorations than with Darwin's own observations: CHATHAM ISLAND. We're going to investigate both palagonite and tuff rings here very shortly. And he understood the basics of palagonite long before petrologists studied the stuff in thin sections and saw the delicate variations he saw. He made conclusions about how these unique volcanoes erupted and eroded that have been confirmed by much later study. He saw how it must have evolved from the basalt itself, and recognized that the tuff cones must have erupted under water. But he didn't just observe this fascinating rock. He looked at the tuff cones dotted along the rocky shores, and saw a marvelous type of basaltic rock that wouldn't even be named until ten years after his visit: palagonite. Yet he saw things no one had eyes to see. And the science of volcanology hadn't really been born yet when Darwin first laid eyes upon the Galapagos. When Darwin began his travels, James Hutton and other Plutonists had only just convinced most of the scientific world that basalt was deposited by volcanoes, not laid down by seawater. Western scientists were only just beginning to grapple with the great age of the earth. Now, keep in mind that Charles Lyell, the father of modern geology, had published the last volume of his Principles of Geology barely a decade before. ![]() Less than ten years after the voyage of the Beagle concluded, he published his findings on the Galapagos and other islands in Geological Observations on the Volcanic Islands, visited during the Voyage of the H.M.S. He scrambled over several of the islands, taking notes and rock samples and puzzling over the origins of what he saw. For a lover of the good science of rock-breaking such as Darwin, it was enthralling. ![]() The hot, dry climate, combined with lava flows that erupted quite recently in geologic terms, presents a sparsely-vegetated and quite lightly eroded rock record. ![]() The Galapagos, a fairly young and still quite active group of volcanic islands, are an ideal playground for a keen young geologist. And the Galapagos Islands would have remained central to his scientific discoveries. If he hadn't become famous as the man who co-discovered evolution, he still would have been noted as one of the fathers of geology. And he discovered things no other person had discovered before understood processes no one before him had figured out. Beagle, he also thoroughly investigated the geology of the places they visited. While collecting meticulous samples of the flora and fauna he encountered on his voyages with the H.M.S. That whole biological evolution thing that Charles Darwin figured out quite often makes people ignore the fact he was a first-rate geologist as well.
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