Exhibitions: The Earth Movers

Ever since artists took to proclaiming that anything is art if the artist says it is, critics have been wondering where the brush would strike next. The instrument they had to fear was the shovel. In Manhattan's Dwan Gallery, the newest frontier is called "Earthworks," and the ingredients on display include dirt, worms, rocks, photographs and written descriptions. "Our original idea," explains the gallery's earth mother, Virginia Dwan, "was just to show earth as a medium, but it's difficult to know where to draw the line."

That is exactly why many artists find the concept so irresistible. Dennis Oppenheim displays a...