Searching Scotland's People for William Spring born 1821, using 1818-1830, there was one result:
Surname: SPRING Forename: WILLIAM Parents/ Other Details: WILLIAM SPRING/CHRISTIAN MENNIE Gender: M Date: 07/06/1818 Parish Number: 251/ Ref: 10 445 Parish: Banchory Devenick
So "Unknown" Spring might be William, not George.