Icy blues of snow- and oceanscapes show a frozen moment of nature's ungraspability. Then, out of the blue, literally, you make out a face in a large snowball--and not just any face, but Karl Marx's. A vague surfer rides roiling swells around the Statue of Liberty, and the cliff face that climbers are scaling is as impossibly angled as an Escher staircase. Now we realize we're in the same intellectual and often very funny terra infirma of Tansey's earlier quasi-conceptual works, as when he reimagined Picasso and Braque as the Wright brothers trying to get their Cubist plane off the ground. That old and new Tansey territory, a land of slippery perceptions, makes up this survey of an important contemporary American painter.