"Les Indes Noires" by Jules Verne is a novel published in 1877. When engineer James Starr receives a mysterious summons from former mine foreman Simon Ford, he returns to the supposedly exhausted coal mines of Aberfoyle, Scotland. Together they discover a vast new seam beneath the abandoned pits, establishing an underground city called Coal-City. But inexplicable phenomena threaten the operation, and deep in the tunnels they find Nell, a young girl who has never seen daylight.
Wikipedia page about this book: en.wikipedia.org/wiki/The_Child_of_the_Cavern fr.wikipedia.org/wiki/Les_Indes_noires