It makes perfect sense that I would have found this one in Maine--tagged as a "mystery box" but in fact a spruce gum box. Associated with logging and lumbering activities, spruce gum boxes, also known as gum books, were usually made from a solid piece of wood, as this one was, with a sliding opening at bottom. These were made by lumberman, typically as gifts for loved ones, most dating from 1850-1920, after which improved transportation allowed them to return home more frequently. Spruce gum, which comes from sap that is hardened into resin, became quite an industry, with Maine the largest and probably first producer of gum with nearly two dozen companies emerging between 1848-1910.
A bit hard to capture in photos, this one, carved to look like a book, features a chip carved pattern on the front which I think might be meant to represent a sprig of Spruce. The back side is painted green, and the top and bottom a mustard yellow, and the spine brown. The slide top opens easily and closes tight.
4 9/16" x 3" x 1 7/8". Overall very good I believe antique condition, with some wear around to the wood and stain mostly around the edges.