Which is which?

Two identical stacks of books, 
side by side on the cabinet top: 
all the same titles, edition and nick.
Ordered identically start to stop.  
One stack is straight, though uneven
in size: all of the angles are neat
as pins. The other's haphazardly 
balanced and skewed. It sits 
solidly, with a crazy grin. 

One of these stacks has been read 
straight through. Every page has 
been turned and explored. The other 
was printed and stacked and sold, 
yet every letter remains unpoured.