“Hardcover books,” for those of you who remember them, are cherished by many, not just because of their relative solidity and heft (relative to e-books), but also because of the many little decorative frills they incorporate. Like marbled, or at the very least quite abstract decorative endpapers. (It must be the lingering popularity of opium that made people love these designs, we think.) The British Library has a collection of decorative papers from the books in its collection. Here are ten of our favorites, although favorites is a weird word here, because while these are beautiful, if you stare at them too long you begin to worry that Cthulhu is going to emerge from the image. You have been forewarned.