….A study by the Smithsonian tells us why old books smell so very lovely (well, I think they do anyway, and it seems I’m not alone!)
It’s to do with a chemical compound in plants called lignin, which is closely related to vanilla. As the book ages, the structure of the paper in the pages starts to break down, releasing that inimitable fragrance.

http://blogs.smithsonianmag.com/smartnews/files/2013/06/06_17_2013_book-smell.jpg