  The distribution of the low-lying QCD Dirac spectrum is analyzed by means of
partial quenched chiral perturbation theory. We identify an energy scale below
which the valence quark mass dependence of the QCD partition function is given
by chiral Random Matrix Theory. This is the the domain where the low-energy QCD
partition function is dominated by the fluctuations of the mass term of the
Goldstone bosons. In mesoscopic physics this domain is known the ergodic domain
and the corresponding energy scale is the Thouless energy.
