Paul S. Boyer. "Underground Railroad." The Oxford Companion to United States History. Oxford University Press. 2001. Encyclopedia.com. 16 Nov. 2009 <http://www.encyclopedia.com>.
Paul S. Boyer. "Underground Railroad." The Oxford Companion to United States History. Oxford University Press. 2001. Encyclopedia.com. (November 16, 2009). http://www.encyclopedia.com/doc/1O119-UndergroundRailroad.html
Paul S. Boyer. "Underground Railroad." The Oxford Companion to United States History. Oxford University Press. 2001. Retrieved November 16, 2009 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O119-UndergroundRailroad.html