  Using two dimensional simulations, we study the formation of structures with
a high-density contrast by magnetohydrodynamic waves in regions in which the
ratio of thermal to magnetic pressure is small. The initial state is a uniform
background perturbed by fast-mode wave. Our most significant result is that
dense structures persist for far longer in a two-dimensional simulation than in
the one-dimensional case. Once formed, these structures persist as long as the
fast-mode amplitude remains high.
