Reference unclear, but it is puzzling. The spelling (Marc) could indicate a French relation of Mary Jane Godwin's. Alternatively, the link to William Godwin the younger's return to Woodford suggests that this may also have something to do with his schooling. The later entries which mention a 'Mark' (for example, 'Mark at home' on 5 September 1818, 'Mark from school', 18 December 1818) suggest that the family have taken on a relative. But there is nothing that clarifies this.