Just to add that although I'm not tracing these Stevensons *, I have noted that Catherine Forbes (bn 1847) had an illegitimate son William Strachan bn 30-4-1869 Cullen by James Strachan who was illeg son of William Strachan & Helen Garden then Gardiner. William Strachan was clearly brought up by his mother. He married twice, lived at Lintmill and Ellieside, and died in 1953.
James Strachan leads back to my 5xgtgdparents James Clark & Elspet Andrew. Helen Garden is sister to Elizabeth Garden then Gardiner who married George Geddes s/o of my 3xgtgdparents Peter Geddes & Margaret Reid. And yes, the surname did change from Garden to Gardiner throughout the family - it happened sometime between 1825 and 1841.
* Margaret Stevenson d/o Alexander Stevenson & Helen McKenzie married my gtgduncle shipmaster James Watson 15 Jun 1881 at Lintmill where they stayed, latterly at Ellieside, until at least his death in 1928. Alexander Stevenson was a mason at Lintmill so I expect that's another connection. James Watson's ship Jane Shearer foundered in 1894; its remains can still be seen at very low tides outside Cullen Harbour wall right in the corner by the shore.