Page 248: Four Classes of Behavior
One-dimensional slices
One-dimensional slices 2
One-dimensional slices through the evolution of various two-dimensional cellular automata. In each picture black cells further back from the position of the slice are shown in progressively lighter shades of gray, as if they were receding into a kind of fog. Note the presence of examples of both class 3 and class 4 behavior that look strikingly similar to examples in one dimension.

From Stephen Wolfram: A New Kind of Science [citation]