A Matter of Days is a book on the young-earth vs. old-earth creationism debate written by astronomer and Christian apologist, Hugh Ross. Ross is an old-earth creationist, meaning he rejects both Darwinism and theistic evolution. He argues that both the scientific and Biblical data support an ancient universe. Not only does he provide evidence for his view, but he interacts with and critiques the arguments and objections raised by young-earth creationists.
If you are interested in the old-earth vs. young-earth debate, this is a must-read book.