Darwinia

In 1912, history was changed by the Miracle, when the old world of Europe was replaced by Darwinia, a strange land of nightmarish jungle and antedeluvian monsters. To some, the Miracle is an act of divine retribution; to others, it is an opportunity to carve out a new empire.

Leaving an America now ruled by religious fundamentalism, young Guilford Law travels to Darwinia on a mission of discovery that will take him further than he can possibly imagine...to a shattering revelation about mankind's destiny in the universe. 
Darwinia is a 1999 Hugo Award Nominee for Best Novel.