EDIT: I added my SketchUp model of the shelves to the 3D Warehouse. You can download it here. —CS
These are pieces of screwed-together 2×12 (which start off at 1-1/2″ thick, and have been planed until pretty). If I recall correctly, there are three, maybe four, screws into the top and bottom of each upright, through the horizontal pieces, all sitting on a screwed-together base. The shelves are secured to the wall with many L-brackets that are bolted to the masonry wall. A lot of visitors bring their children to the storefront, so we wanted to make sure the unit could be safely scaled by a gorilla.
And while they looked ridiculously capacious when Brendan Gaffney finished constructing them from Christopher Schwarz’s drawing, they were full up with woodworking tomes in just an hour or so.
The drawing below – plus knowing that the pieces are from 2x12s – should provide enough detail for you to easily adapt such a system to your own library wall needs.