Look at the picture below

Early in the story when tom finds an indian skull in the woods which he kicks in temper. the devil then makes his appearance and, as tom surveys him, he notices that the devil is neither "negro" nor "indian." in fact, he has a "swarthy" complexion and is "begrimed with soot."

Its in the national history museum and you can't se the original because its locked away in a vault 

Answer volcanic outgassing;