APA (7th ed.) Citation

Roberts, C. G. D. (2006). Earth's Enigmas: A Volume of Stories. Project Gutenberg.

Chicago Style (17th ed.) Citation

Roberts, Charles G. D. Earth's Enigmas: A Volume of Stories. Project Gutenberg, 2006.

MLA (9th ed.) Citation

Roberts, Charles G. D. Earth's Enigmas: A Volume of Stories. Project Gutenberg, 2006.

Warning: These citations may not always be 100% accurate.