Hi...My Great great grandfather was Robert Deppa, born in 1842 in Dunbar, East Lothian Scotland. I believe that he may be the brother to your James? I was also interested in finding out some information about James Deppa and Marion McKenzie as they turned up after looking at some info in the family bible. Im very new to looking into my family's geneology, I hope to hear from you.
Thanks,
Kelly.