Hi Jean, many many thanks for the information on Margaret Davidson - I hadn't come across it before. The children's names confirm that it is indeed my ancestral lineage.

The name "Welch" or occasionally "Welsh" appears quite frequently as a middle name in this particular lineage. I'm in the process of trying to discover its derivation and I've made a couple of links recently. Ann Hay, the sister of "my Mary Hay", and daughter of David Hay & Margaret Davidson married David Welch 31 Jul 1820. Their eldest child was Robert Greig Welch b. 29 Sep 1840. I think that you've definitely found his MI, so many thanks again!
I wonder if I could possibly trouble you some more, this time on an associated lineage. My 3rd great grandfather was James Rae. I have a document that states he was a forrester at Denhead of Balhaggerty in Dec 1842. I think he died before the 1851 census. He was born abt 1791 in Benholm parish, possibly Garvock. I don't know anything about James's parents.
James Rae's second wife was Isobel Watson, b. abt 1799 at St Cyrus and died at Braehead, Johnshaven 2 Sep 1889. Her parents were John Watson & Mary Croll. John was born abt 1758 and Mary abt 1762 both in Benholm parish. I think John died before the 1841 census. Mary appears in the 1841 census living with James & Isobel at Denhead in the civil parish of Garvock, but not in the 1851 census.
Again, any information on the above would be greatfully received.
Many thanks once again
Stewart