Alexander Matheson and his wife Margaret came from the area near Helmsdale, on the Scottish coast of Sutherland Shire.
There is a family of Mathesons which could be theirs, in the records for Midgarty, near Helmsdale. Thomas Matheson said he
was born at Helmsdale when he emigrated to Australia.
I have found the following children for this family - dates are baptisms.
Residence - Midgarty (near Helmsdale)
Patrick 14 Aug 1805
12 July 1807
Thomas 20 Sept 1809
Gorden 18 Jun 1812
3 July 1815
Adam 3 Feb
Thomas married Mary Straith (or Strath) in Aberdeen, before leaving for Australia, and secondly, Jane Wilkinson, in Australia.
You can see the file by clicking on the link below.