Well, I'm amazed and thrilled at the responses to this thread after such a long time - many, many thanks to Tara and to Dathai for all your work; you've both provided some valuable information which has helped me chip away at this particularly stubborn brick wall, and I very much appreciate it. Of course thanks also to Fiona for resurrecting this thread - I'm delighted to have found a new cousin

Tara, you're right - they are the family from Brown Street. Since I first posted this I've been in touch with a couple of 3rd (I think!) cousins in Ireland, and have confirmed that James (my great grandfather) is indeed the son of William Deering and Anne Gore, who apparently came from Baltinglass, although I haven't found any record of them there yet.
I'm still looking for the elusive marriage of James and Julia (Dathai, I think it is 'my' James in Manchester, but no luck with the English marriage records), but with new information coming to light all the time, I'm hoping that I'll find it sooner or later!
Fiona - I've sent you a pm!
Thanks again everyone
