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The best information I have regarding your ancestor comes from my own lineage, as follows. Around 1750, James Mundell and his son, James, came to the Philadelphia area from Ireland. The elder James had left behind a wife and at least two daughters, bringing his son to America to seek a new life. He was a wheelwright, making mill wheels. He apprenticed the younger James to a cooper. After he had saved enough money, he returned to Ireland to bring the rest of the family over. His ship went down at sea. The younger James married Margaret Garrett, daughter of John Garrett, a miller. They took up housekeeping in NewCastle County, Delaware. Later, they joined a group of young couples moving to Greene County, PA. There they took a quarter section as a homestead. James opened a cooper's shop in Ceylon. A third James, son of the cooper, inherited the family homestead. He was a farmer and a whiskey distiller. His son, Abner next inherited the homestead, followed by his son, Abner Breckenridge Mundell. It was this Abner B. Mundell who married Anna Speers Stirling. She and a brother were born in Frostburg, Maryland to parents who were Scottish immigrants. One of their sons, Edward Theodore, was my grandfather. His son, Clyde Stirling Mundell, was my father.
I hope this is of some help. If you have more specific questions, I will try to help.