As I was at the historical society doing some reasearch for my seminar, I had the chance to take a break and check out the Sinclairs of Stevenston. This source said that Matthew Sinclair of Longformacus, 9th of that line, had a grandson, John Sinclair, a wealthy merchant of Edinburgh. He purchased the lands of Stevenston in Haddington, adding other lands in Haddington, Edinburgh, and Berwick, becoming a baronet of Nova Scotia in 1636. His grandson, John, succeeded him, being followed by his brother Robert. It is Robert's son, Jonh, who is mentioned by George Bogle. Perhaps, this branch purchased the lands from the branch mentioned in "Saint Clairs of the Isles."
Click here to see page 1 of that reference in "Saint Clairs of the Isles."
