Usually bookstacks. stack(def 4).
Origin of bookstack
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Examples from the Web for bookstack
Historical Examples of bookstack
He turned again to the bookstack, and said: "I will hear the defence."
The creature on the bookstack was nodding and signing to Fiona, but she was too engrossed with a single thought to notice him.