Edmond Dantes and Monte-Cristo's Cauther: Two Sequels to Dumas' Count of Monte-Cristo

According to Wikipedia: "The Count of Monte Cristo (French: Le Comte de Monte-Cristo) is an adventure novel by Alexandre Dumas. It is often considered to be, along with The Three Musketeers, Dumas's most popular work." These sequels were written by a 19th-century American author.