Paul Proulx is certainly one of the most insightful and prolific of the many scholars who share Frank Siebert's fascination with the Algonquian languages, their histories, and their implications for the reconstruction of the social and cultural histories and prehistories of the Algonquian peoples and their precursors. His description of some encounters with Frank Siebert follows.
Proulx, Paul. "Siebert and His Correspondence." Maine History 37, 3 (1998): 99-101. https://digitalcommons.library.umaine.edu/mainehistoryjournal/vol37/iss3/9