As you search in the online catalog, watch for the words "personal narratives," "diaries," "correspondence," "pamphlets," and "sources" as part of the subject headings; these may point you to published primary sources in the library collections.
You can also search for these words, using the "Subject keywords" search, for example:
Other clues may be buried in the title, authorship, date of publication, etc.
Examples of some published primary sources in Neilson: