MLA

Roberts, Charles George Douglas, Sir, 1860-1943. Earth's enigmas, by Charles G. D. Roberts ... illustrated by Charles Livingston Bull. 1903. https://collections.library.yale.edu/catalog/10545536.

APA, 6th edition

Roberts, Charles George Douglas, Sir, 1860-1943. (1903)[Earth's enigmas, by Charles G. D. Roberts ... illustrated by Charles Livingston Bull]. https://collections.library.yale.edu/catalog/10545536.