Eight mirrors, buttressed from both sides by basalt rocks, converge in a square formation. The rocks were gathered from an area near Paterson, New Jersey, an area renowned for trap rock quarries. The rocks are the primary “substance” of the work, yet their structural purpose lies in service to the mirrors, or the “non-substance.” In the center of the square a portion of the gallery floor is left bare, revealing the rocks’ impermanent placement both in the gallery and in the site from where they came. In the relatively simple construction, Smithson poses many questions about the origin, perception, and substance of art.