jwaugh, How did you get on with finding your Cormachan's?
I ask as I have just come across this surname in my family tree. A Margaret Cormachan was mother of children to John Bell of Glenfield, Crumlin, Antrim. Three of the children (there may have been more) were Allen b.1841, Catherine b. 1845, and John b.1846. All three born in Crumlin or thereabouts and immigrated to New Zealand in the 1860's.
I have not been able to determine if John and Margaret were married. Nor have I been able to find out anything about the Cormachan's. Google led me here.
Kind regards
SpudKiwi