Hi,
Have belatedly looked at the Scottish board and noticed that Alexander may have had a brother called George. Doing a parent search on the IGI I found an Alexander Jamieson born to William Jamieson and Jane Key in Londonderry City on 18 Feb 1871. I also found that a George Jamieson was born to a William Jamieson and Jane McKey on 12 Aug 1865. The parish for both was Glendermot.
William Jamison (sic) married Jane Key on 26 Nov 1864 in St. Columbs Church of Ireland, Londonderry City.
Regards