My Cowan family of Dundee turn out to have Irish antecedents; there appear to have been a lot of Irish immigrants in Dundee, but they seem to have been amongst the poorer part of the population, and amongst people brought up in Dundee having Irish ancestors doesn't seem to be something to be owned up to. They're still there, though. Mark and Bridget were born and married in Sligo, leaving for Scotland some time after 1845.
William's Birth Certificate Thomas's Death Thomas and Betsy's Marriage Thomas's Birth Certificate Mary Cone's Birth Certificate. In 1855, oh yes. Mark's Death Certificate