Collector's Library of the Unknown is a 6-book series first released in 1882 with contributions by Ignatius L. Donnelly, Upton Sinclair, and 3 others.
1882 • 2 Readers • 490 pages
1882 • 1 Reader • 303 pages
1929 • 1 Reader • 208 pages
1966 • 1 Reader • 350 pages
1940 • 1 Reader • 255 pages