Hi Mirrin,
I read with interest this thread, although it is over a year old now. I just happened to be searching the web last night as I couldn't sleep. It has been a few year since I did family history research and was fascinated by this discussion. My name is Mary-Anne Jones (nee Forrest). I note your thread listed my aunties and uncles but not my dad. Sarah and Robert had 10 children in Queensland, my dad (Ambrose) and Peter were the only two who married and had children. I'm not sure if you solved your mystery, but the John Forrest you talk of who emigrated to Australia is my ancestor. He is my father's grandfather. I have information on him, but nothing about an illegitimate child. My details have him at Cumbusnethan when he married in 1866, married to Elizabeth Henderson. He had several changes of addresses throughout his life. He is the same person who is in Toowong cemetery and was born (6th child) to Rachel Millar and Robert Forrest in October 1844 at Carluke. He came to Australia. left England 18 Sept 1888 and arrived on the Dacca at Brisbane 12 Nov 1888. I'll leave it there for now. I'm interested about your quest and whether you eventually solved it. Also, interested in where the connection started in terms of my g-grandfather. I gather you live in Scotland? I'm in Queensland Australia.
