  A giant Nernst signal was recently observed for fields near crystallographic
directions in (TMTSF)$_2$PF$_6$. Such large Nernst signals are most naturally
associated with the motion of pancake vortices. We propose a model in which
phase coherence is destroyed throughout the sample except in planes closely
aligned with the applied field $\bf H$. A small tilt above or below the plane
changes the direction and density of the penetrating vortices and leads to a
Nernst signal that varies with the tilt angle of $\bf H$ as observed. The
resistance notches at magic angles are understood in terms of flux-flow
dissipation from field-induced vortices.
