During the maritime fur trade era of the early 19th century the islands were a source of fur seal skins, and the Juan Fernández fur seal was nearly driven to extinction. In his book, "Two Years Before the Mast" (Chapter VII), Richard Henry Dana, Jr. described the islands as he found them circa 1834. At this time the main island was being used as a penal colony. However, when Dr John Coulter visited the penal colony in the early 1840s, he reported it deserted after the convicts had risen up and killed the soldiers who had held them captive. The prisoners fled to mainland Chile, where they were later hunted down and shot. The story appears in Coulter's book "Adventures in the Pacific" (1845). In 1908, the islands were visited by the Swedish Magellanic Expedition and Carl Skottsberg is believed to have been the last to have seen the "Santalum fernandezianum" tree alive.