Defoe's Tour through Great Britain—Etymology of Armagh

In your sixth number some extracts are given "from a once popular, but now forgotten work," *A Tour through Great Britain*, by a Gentleman, 1724. I have an edition of it dated 1753, which was sent me by a respectable London bookseller as one of the works of Defoe. Can you or any of your friends inform me whether it is really to be attributed to that writer? Perhaps also one of your philological correspondents, acquainted with the Gaelic or Celtic language, might favour me with his opinion as to the etymology and meaning, if any, of *Armagh* in Ireland.