Complex sentence: Willem Janszoon returned to the Netherlands apparently in the belief that the south coast of New Guinea was joined to the land along which he sailed, although his own chart did not verify his claim to have continuously followed the coastline where the Torres Strait is found.
Split into simpler sentences: Willem Janszoon returned to the Netherlands apparently in the belief that the south coast of New Guinea was joined to the land along which he sailed. On the other hand his own chart did not show that he claimed to have continuously followed the coastline where the Torres Strait is found.