MLA

Wallace, Susan E. (Susan Elston), 1830-1907. Letter : Crawfordsville, to "Dear Sir". Box 6, folder GROUP 105, F-2. 1898 Mar 7. https://collections.library.yale.edu/catalog/2014446.

APA, 6th edition

Wallace, Susan E. (Susan Elston), 1830-1907. (["Box 6, folder GROUP 105, F-2"])(1898 Mar 7)[Letter : Crawfordsville, to "Dear Sir"]. https://collections.library.yale.edu/catalog/2014446.