Hart, R. L. (2019). Glenhill Farm: The history of a family estate : as revealed in the correspondence between Brognard Okie and Ernst and Mary Behrend. Penn State Erie, the Behrend College.

Hart, Richard L. Glenhill Farm: The History of a Family Estate : As Revealed in the Correspondence Between Brognard Okie and Ernst and Mary Behrend. Erie, Pennsylvania: Penn State Erie, the Behrend College, 2019.

Hart, Richard L. Glenhill Farm: The History of a Family Estate : As Revealed in the Correspondence Between Brognard Okie and Ernst and Mary Behrend. Penn State Erie, the Behrend College, 2019.