"Whenever any citizen of the United States discovers a deposit of guano on any island, rock, or key, not within the lawful jurisdiction of any other Government, and not occupied by the citizens of any other Government, and takes peaceable possession thereof, and occupies the same, such island, rock, or key may, at the discretion of the President, be considered as appertaining to the United States."
That's from the Guano Island Act, passed by Congress in 1848. Link.
I'm doing some research on soil phosphorus for my soil science class's final project.
I'm using this excellent book which directed me to this fine webpage which led me to this fascinating story about bat guano which prompted a FindLaw search.
You just couldn't assemble information at that rate before the 21st century.