On 8 July, they stopped at St. Helena for six days. Darwin took lodgings near Napoleon's tomb, and when writing to Henslow asking to be proposed for the Geological Society, he mentioned his suspicions "that differently from most Volcanic Islds. its structure is rather complicated. It seems strange, that this little centre of a distinct creation should, as is asserted, bear marks of recent elevation." With a guide, he wandered over the island, noting its complex sloping strata showing fault lines, interlaced with volcanic dykes. He examined beds high on the hill that had been taken as seashells showing that St. Helena had risen from the ocean in recent times, but Darwin identified them as extinct species of land-shells. He noted that woodland had been destroyed by goats and hogs that had run wild since being introduced in 1502, and native vegetation only predominated on high steep ridges, having been replaced by imported species.