They've torn down some of the older buildings on Fourth Street (I can't for the life of me recall what used to be there) and the side of the Pepper Building reveals the mason's equivalent of dust swept under the carpet. The space between the walls was just filled in willy-nilly, with little rhyme or reason and probably in very little time. This has been the practice of masons since Ancient Rome and earlier, making these in-between spaces a treasure trove for archeologists, as everything under the sun might get tossed in to take up the space.
Here is a closer view of the crazy work. Click the images for a larger version.