"Contains some 100 primary source documents that include ledgers, travel accounts, autobiographies, official reports, memoirs, logbooks, patents, letters, articles of agreement, and corporate minutes"
Suggested terms to look for include - diary, diaries, letters, papers, documents, documentary or correspondence.
Combine these these terms with the event or person you are researching. (example: civil war diary)
Also search by subject for specific people and events, then scan the titles for those keywords or others such as memoirs, autobiography, report, or personal narratives.