  We formulate a framework for the depolarization of linearly polarized
backscattered light based on the concept of geometric phase, {\it i.e} Berry's
phase. The predictions of this theory are applied to the patterns formed by
backscattered light between crossed or parallel polarizers. This theory should
be particularly adapted to the situation in which polarized light is scattered
many times but predominantly in the forward direction. We apply these ideas to
the patterns which we obtained experimentally with backscattered polarized
light from a colloidal suspension.
