Complex sentence: He also asserted that Atlantis would "rise" again in the 1960s (sparking much popularity of the myth in that decade) and that there is a "Hall of Records" beneath the Egyptian Sphinx, which holds the historical texts of Atlantis.
Split into simpler sentences: He also asserted that Atlantis would "rise" again in the 1960's (sparking much popularity of the myth in that decade). It is also believed there is a "Hall of Records" beneath the Egyptian Sphinx which holds the historical texts of Atlantis.