  Changes: figures added in postscript form, Eq. (7) and various typos
corrected. We examine the effect of an impurity on the nearby tunneling
conductance in an anisotropically-gapped superconductor. The variation of the
conductance has pronounced spatial dependence which depends strongly on the
Fermi surface location of gap extrema. In particular, different gap symmetries
produce profoundly different spatial features in the conductance. These effects
may be detectable with an STM measurement on the surface of a high-temperature
superconductor.
