APA (7th ed.) Citation

Darwin, C. (2003). Geological Observations on South America. Project Gutenberg.

Chicago Style (17th ed.) Citation

Darwin, Charles. Geological Observations on South America. Project Gutenberg, 2003.

MLA (9th ed.) Citation

Darwin, Charles. Geological Observations on South America. Project Gutenberg, 2003.

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