Alison, and David Gange,
With all due respect, you may be barking up the wrong tree. If both of your families are of England then it is unlikely that you descend from Marquis de Ganges. Visit my website (address you will have to type in order to get there)http://www3.nb.sympatico.ca/guissem/
I would suggest tracing your tree as far back as possible. This will give you some idea of where your ancestors came from.
I am not an expert but do have thirty years or more of research on this subject. In addition have published a number of works on the subject.
Marilyn Shaw-Guisset (email@example.com