Eric
 
I'm not too sure about place-names in 'ham' having a Norse derivation.
 
I believe that 'ham' is one of the earlier place-name elements to be found in Old English charters of the seventh century;  'tons' as a rule, occur in later charters.
If anyone is interested in this, the authorities to consult are Joliffe, Stenton and Granville.
 
I haven't really looked at the distribution of 'hams' in Britain, so I can't say whether they predominate in the north. I do know that they occur far less frequently than the 'ton' settlements and that the implications of this could be that they were early administrative or political centres for their respective regions.
 
Anyhow, if there is a chance for an informed discussion on this, I would like to hear other opinions.
 
Cheers
Jed Mc Harg