Intimate letters and manuscripts written by Mark Twain, as well as photographs of the American author, will be sold by Sotheby's in June.

Among them is a 64-page, handwritten document called "A Family Sketch" (est. $120,000 to $180,000) that honors his daughter, Olivia, who inspired some of his characters.

Twain wrote, "In all things she was intense: in her this charateristic was not a mere glow, dispensing warmth, but a consuming fire...."

The entire collection is estimated to fetch between $750,000 and $1.2 million.