Complex sentence: However, in follow up correspondance Gutscher indicates that the Island could not have been Atlantis, referring to Plato's description of a Bronze Age society, which Spartel could not have supported at the time.
Split into simpler sentences: However, in follow up correspondance Gutscher indicates that the Island could not have been Atlantis. He references Plato descriptors of a Bronze Age society, which Spartel could not have supported at the time.