The frontier interpretation of American history with which Professor Frederick Jackson Turner captivated and intrigued the observers of American development more than forty years ago still retains its fascination. Professor Turner saw the American frontier as an area in which American society was constantly being rebuilt, each time shaped by special problems: “American social development,” he wrote, “has been continually beginning over again on the frontier.” It was on this theme that Professor Turner based his most striking contention that “The existence of an area of free land, its continuous recession, and the advance of American settlement westward, explain American development.”