MLA

Stieglitz, Alfred, 1864-1946. Letters. Box 225, folder 4007-4017. 1969-70. https://collections.library.yale.edu/catalog/10575722.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 225, folder 4007-4017"])(1969-70)[Letters]. https://collections.library.yale.edu/catalog/10575722.