Baseball and Jackie Robinson: About the Collection.

http://memory.loc.gov/ammem/jrhtml/jrabout.html

This collection, fully titled Baseball, the Color Line, and Jackie Robinson, pulls together historical materials from different sections of the Library of Congress. You can browse it using a timeline segmented into five different periods: Drawing the Color Line (1860s-1890s), Barnstorming & the Negro Leagues (1900-1930s), Breaking the Color Line (1940-1946), Robinson as a Dodger (1947-1956), and Robinson's Later Career (1956-1972).

Referenced in:
Baseball In Pennsylvania
On the Other Side of the Color Barrier: Segregation and the Negro Leagues