Brown, R. W. (1940). "New species and changes of name in some American fossil floras". Journal of the Washington Academy of Sciences. 30 (8): 344–356. JSTOR24529454.
Gini-Newman, Garfield; Graham, Elizabeth (2001). Echoes from the past: world history to the 16th century. Toronto: McGraw-Hill Ryerson Ltd. ISBN9780070887398. OCLC46769716.