  The improved Wilson quark action - the clover action - is constructed to have
smaller discretization errors than the normal Wilson quark action. We test this
in a quenched spectroscopy computation on 6 lattice ensembles with spacings
from 0.15 to 0.43 fm. To ensure that the dominant scaling violations come from
the fermions we use an $O(a^2)$ improved 6-link $SU(3)$ pure gauge action. We
find evidence that fermionic scaling violations are consistent with $O(a^2)$
for clover fermions and $O(a)$ with a nonnegligible $O(a^2)$ term for standard
Wilson fermions. This latter mixed ansatz makes a reliable continuum
extrapolation problematic for Wilson fermions. For clover fermions, on the
other hand, we obtain accurate predictions for hadron masses in quenched
continuum QCD. We find that the slopes of the scaling violations are roughly
200 MeV for both Wilson and clover fermions.
