Urban, William. Where was Nicholas Earp in 1849–50?. Western Illinois University Archives. Monmouth, Illinois: Monmouth College. [2015-11-06]. (原始内容存档于2016-03-05).
Urban, William. Where was Nicholas Earp in 1849–50?. Western Illinois University Archives. Monmouth, Illinois: Monmouth College. [2015-11-06]. (原始内容存档于2016-03-05).