The 'Fasti' is the roll of Scottish Ministers and their succession from the Reformation.In the volume containing entries for the North Isles, and listed under Rousay and Egilsay, two small islands north of the Orkney Mainland, we find John Williamson, for me a second cousin, once removed. His entry reads as follows:
JOHN WILLIAMSON, born Greenock, 8th Oct. 1886, son of Joseph W. and Janet M'Illhagga; educated at Bible Training Institute, Glasgow, Univs. of Glasgow and Edinburgh; assistant at Newhall, Glasgow, 1914-15; on War Service (Ministry of Munitions) 1915-17; ord. to Free Church, Culter, Lanarkshire, 21st May 1917; trans. and adm. 8th Feb. 1921; trans. to Kirkfieldbank, Lanark, 5th Dec. 1922. Marr. 5th Aug. 1912, Mary Cecilia Cummings, Blairmore, Argyll (born 23rd April 1888), and has issue - Mary Cecilia Janet, born 22nd Nov. 1913; John Alexander, born 20th Feb. 1920; Charles Kerr, born 1st June 1924.
The only detail to note is that his mother's surname is misspelled. It should read McIlhagga (correct on John's birth entry in the Statutory Registers on ScotlandsPeople). Janet was the sixth daughter of John McIlhagga and Mary Stewart (b. 1866/7) of Greenock. John had migrated from Ballycloughan in County Antrim, the second son of William McI. and Agnes McCosh.