It is Archibald's cousin Rosey who I 'trawled' this week as a McElhaggo from FamilySearch. She was in a Ireland Births and Baptisms, 1620-1881 record as the mother (Rosey McElhaggo) of a female child born 10th March 1864. As there is no name for the child we must assume that she died at birth. I knew of Rosey/Roseanna/Rose and her husband John Warwick, but the child is an addition to my knowledge. Rosey was one of the daughters of John McIlhaggo, another farmer at Maxwell's Walls. He possibly married an Agnes. We may surmise this from an Agnes McIlhaggo signature as a witness at the marriage of Rose's sister Mary, to William Christie on 30th August 1859. The third daughter was Ellen who married Robert Scroggy on 16th March 1868. In the FamilySearch trawl there was one other McElhaggo, a John Wilson, born 1865 who died in 1867 in Antrim District. All other examples of the variant McElhagga which crop up seem to be a simple misreading of McIlhagga, and McElhaggo a misreading of McIlhaggo.
The same thing applies to most uses of the variant name McHagga. All the examples FamilySearch gave me, except two, were already known to me as McIlhagga, and indeed all came from my own family tree! The two exceptions are of some interest. First, Rachel McHagga is named as the mother of John Francis, born 29th March 1866. Rachel's husband was also John Francis. Calculating backwards, Rachel would have been born about 1840. I have no Rachel in my Indexes who would fit this date. The second interesting thing here is that John Francis' birth place is given as Bathgate, West Lothian. A large family of McIlhaggas have lived in Bathgate since about 1900 but 1866 is a very early date to find a member of our clan there. I am wondering if it is a transcription error. I must check.
The other McHagga is Elizabeth, daughter of John and Jane, who was born even earlier that Rachel, on 11th December 1808 in Saltwood, Kent, England. Not only would this give us a very early date, perhaps 1780, for father John's birth year, but to find the family in South East England is very strange. There is a John and Jane McElhager or McIlhago of the right dates - she was Jane McCarley - who are to be found as parents in the Baptismal Registers of the First Presbyterian Church, Broughshane, County Antrim, Northern Ireland, but I have to say that I have no evidence that they migrated over the Irish Sea, or that they became known as McHagga.