The "Two Books" view of divine revelation not only has a long pedigree in Christianity but has been part of our community's intellectual heritage since before its official formation. In 1837, John Thomas wrote:
The Advocate: For the Testimony of God as it is Written in the Books of Nature and Revelation CONDUCTED BY JOHN THOMAS, M.D. The invisible attributes of God, even his eternal power and divinity, since the creation of the world, are very evident; being known by his works.—PAUL. All scripture given by divine inspiration, is profitable for doctrine, for conviction, for correction, for instruction in righteousness: that the man of God may be perfect—completely fitted for every good work.—PAUL. 
As these words were written over twenty years before Darwin published the first edition of The Origin of Species, any assertions that the "Two Books" approach was invented solely to legitimate evolutionary creationism are demonstrably false. The concept of God revealing himself through two complementary "books" has nothing to to with evolution, but rather recognises the fact that if the Bible is a reliable guide to God's purpose with humanity, then the natural world should likewise be a reliable witness to its own origins.