  We formulate and solve a model problem of dispersion of dense granular
materials in rapid shear flow down an incline. The effective dispersivity of
the depth-averaged concentration of the dispersing powder is shown to vary as
the P\'eclet number squared, as in classical Taylor--Aris dispersion of
molecular solutes. An extensions to generic shear profiles is presented, and
possible applications to industrial and geological granular flows are noted.
