Subject Heading Searches in WU Catalog. Subject headings bring similar materials together under one set of terms.
Books can be secondary sources that comment on primary sources or books can be primary sources themselves.
The subject headings below which have the subdivision -- sources or description and travel - are themselves primary sources.
The subject headings which have the subdivsion -- dictionaries, chronologies, encyclopedias, bibliographies - are " key tools and works available to search out the secondary literature."