THINKING ABOUT Jeff Wall’s most recent exhibition in New York, a show of light-box pictures at Marian Goodman Gallery last spring, has led me to reflect on the more philosophical or, say, ontological turn his work has taken during the past four or five years. The central image in the show was Fieldwork. Excavation of the floor of a dwelling in a former Sto:Io nation village, Greenwood Island, Hope, University of California at Los Angeles, working with Riley Lewis of the Sto:Io band, 2003. For all the information the title provides, it doesn’t quite say everything. The picture offers us a largely downward view into and across a clearing in a forest where two men are at work.