This most interesting surname,of Old Scandinavian origin appears widespread
in the Lake District of England, and is a topographical name, for a "dweller by
the bank or ridge of a ravine" from the Old Norse "gil" meaning ravine or narrow
valley, and the Old Danish or Old Norse "banke" meaning bank or ridge. The
surname is widespread in Cumberland , Yorkshire, and Lancashire as is shown by
early recordings of the name in these regions. There is however a puzzle of why they family used two names Banks and Gillbanks, this led to some difficulty in tracing back to Isaac, how I solved the puzzle is explained here