  Let $X$ be a smooth projective variety of dimension $n$, and let $E$ be an
ample vector bundle over $X$. We show that any non-zero Schur class of $E$,
lying in the cohomology group of bidegree $(n-1, n-1)$, has a representative
which is strictly positive in the sense of smooth forms. This conforms the
prediction of Griffiths conjecture on the positive polynomials of Chern
classes/forms of an ample vector bundle on the form level, and thus strengthens
the celebrated positivity results of Fulton-Lazarsfeld for certain degrees.
