Complex sentence: Narváez is said to have given the name Punta de Gaviola to the southeastern end of the island and that over time Gaviola was corrupted into Gabriola and applied to the whole island.
Split into simpler sentences: Narváez is said to have given the name Punta de Gaviola to the southeastern end of the island. Over time, "Gaviola" may have been corrupted into "Gabriola" and applied to the whole island.