Harrison, Horace W. (2003). 19th Century Registered Postmarks of Canada’s Railway Post Offices.

In the months before his death, Horace Harrison had completely torn apart his exhibit of registered letter stamps and the corresponding exhibit of covers. His exhibit of Registered Railway Post Office postmarks survived him, however, and in 2003 Jean and Bill Walton scanned the exhibit pages so they could be published as Volume 31 of the BNAPS Exhibit Book Series. In his introduction to the exhibit Horace wrote that “these are among the scarcest postmarks in Canadian Philately”.