Charles Darwin, in 1838, was the first naturalist to write about Tierra del Fuego, the southernmost tip of South America. He noted that the rocks around Ushuaia included metamorphic schists, phyllites, gneiss and granite. He also noted the change of direction of the Andean Cordillera from a North/South direction at the Straits of Magellan to an East/West direction south of the Beagle Channel. How right he was!
Today scientists studying the complex geology of this region recognize geologic processes including volcanism, stretching, compression and faulting where the oceanic Nazca plate wedges itself under the continental South American plate.
Sediments in this sample derived from the decomposition of rocks along the shoreline. Other grains no doubt originated in the Andes and made their way to the shore via the many rivers.