The obvious use of a vertical stack of books as a bookend on an open bookshelf (that is, open on the sides), in place of, for example, a flower pot or a glass jar filled with pennies or a large matryoshka doll (assembled) needs no defense (it is a question merely of function, insofar as the vertical stack cum bookend is itself of the substance of the shelves’ intended contents).
It is those book stacks that occur within a row of horizontal books to which I advert. I see two important purposes: (I) as a convenient means of adding variability to the capacity of a shelf, for one might add books to the stacks without expanding the (horizontal) dimensions of the shelf itself (an impossibility for books placed on their ends in the usual manner once a shelf has reached its [horizontal] capacity), and (II) (A) to divide books by subject—for example, a small stack on post-Vietnam U.S. history (including All the President’s Men, Vidal’s Imperial America, Lawrence Wright’s The Looming Tower, and so on) may be used to effectively separate my U.S. history collection from the beginning of a (meager but growing) collection on Narratology (beginning with Barthes’ Image-Music-Text and Benjamin’s Illuminations) situated in the usual manner, that is, on their ends in a horizontal arrangement—or (B) to represent (a) a subsection, when said subsection has both (i) appropriate distinctiveness and (ii) sufficient number (but not too many, as determined by the height of the shelf) of titles to warrant its own stack—for example, the several books within my U.S. history collection on the Civil War (including McPherson’s classic Battle Cry of Freedom, David Potter’s The Impending Crisis, James Ronald Kennedy’s controversial The South Was Right!, and so on), or (b) a subject of its own, such as a stack, say, of books related to the rich subject of lexiphanicism (assuming, of course, there are enough [but not too many] titles to warrant the stack). We add to this, as mentioned supra, the utility of the stacks as bookends, not to mention the aesthetic gain of the visual interruption of the monotonous uniformity of a horizontal line of books, and the value of occasional vertical book stacks in any library is, I believe, apparent.
The reader, after a moment of silent deliberation, declaims that the stacks present a problem, namely, one of extraction, if, that is, the book in question happens to be near the bottom, or base—or plinth—of its stack-tower.
It is true, I reply. It is the one flaw.