I have a census reference on a Benjamin Franklin Markley that lists him as B. Franklin Markley - if he went by his middle name, it's likely that he used Frank as a diminutive.
My great-grandfather was a Benjamin Franklin Markley married to Anna Brubaker Good. He went by the name Frank. His parents were John Markley married to Anna (no last name known). My mother says that John was English rather than German. They lived in Martic in the middle 1800s.