Book excerpt: Social and religious historians have conducted much research on Scottish colonial migrations to Ulster; however, there remains historical debate as to whether the Irish Sea in the seventeenth century was an intervening obstacle or a transportation artery. Vann presents a geographical perspective on the topic, showing that most population flows involving southwest Scotland during the first half of the seventeenth century were directed across the Irish Sea via centuries-old sea routes that had allowed for the formation of evolving cultural areas. As political or religious motivational factors presented themselves in the last half of that century, Vann holds, the established social and familial links stretched along those sea routes facilitated chain migration that led to the birth of a Protestant Ulster-Scots community. Vann also shows how this community constituted itself along religious and institutional rubrics of dissent from the Church of England, Church of Scotland, and Church of Ireland.