  Convective motions in a fluid layer are affected by its orientation with
respect to the gravitational field. We investigate the long-term stability of a
thermally-stressed layer of a binary liquid mixture and show that pattern
formation is strongly affected by marginal inclinations as small as a few
milliradians. At small Rayleigh numbers the mass transfer is dominated by the
induced large scale shear flow, while at larger Rayleigh numbers it is
dominated by solutal convection. At the transition, the balance between the
solutal and shear flows gives rise to drifting columnar flows moving in
opposite directions along parallel lanes in a Super-Highway configuration.
