The oscillatory modes of a sharply bounded plasma which involve surface charge are studied by a method which includes the behavior of the surface charge. It is found that these modes are "quasi· oscillations" -they do not persist indefinitely, eventually being destroyed by muliistreaming. They are inherently nonlinear, not even possessing a line~zeable limit if the density gradient is made finite. An important conclusion is that the surface charge modes probably play no role in laboratory experi· ments on the scattering and a-c probe resonances. On the other hand, there may be situations in which the surface charge modes would contribute importantly to an experiment, but would not be predicted by a linearized theory.