Complex sentence: He wrote extensively on the works of J. R. R. Tolkien as well as on Elizabethan English drama, philosophy, religion, and medicine; and the Franciscan missions of 18th-and 19th-century California.
Split into simpler sentences: He wrote extensively on the works of J. R. R. Tolkien as well as on Elizabethan English drama, philosophy, religion, and medicine. He also authored books on the Franciscan missions of 18th-and 19th-century California.