  Motivated by their gravitational-wave driven instability, we investigate the
influence of the crust on r-mode oscillations in a neutron star. Using a
simplistic model of an elastic neutron star crust with constant shear modulus,
we carry out an analytic calculation with the main objective of deriving an
expression for the ``slippage'' between the core and the crust. Our analytic
estimates support previous numerical results, and provide useful insights into
the details of the problem.
