It's a mystery, Peter, because both Peters are listed as being the children of Peter & Sarah.
I've just this morning stumbled upon another mystery:Sarah gave birth to Joseph on the Darling Downs on 12 September, 1848, the same day as Elizabeth Blair was born to her parents, John Blair & Mary (nee Pegg).Sarah's husband, Peter Pegg, had drowned in the Clarence River in 1846!(After his death, Sarah had become the station housekeeper for Blaxland.)I wonder who Joseph's father was?
Talk about a coincidence, I just found a query online today from a descendant of Joseph, after discovering that mystery!