  In magnetic measurements on Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi-2212)
single crystals, a general peak with a dynamical feature on both $S-H$ and
$S-T$ curves was found with S the magnetic relaxation rate. At higher fields,
the characteristic exponent $\mu$ becomes negative, together with the positive
curvature of $logE$ vs. $ logj$ and the scaling based on the 2D vortex glass
theory or plastic creep theory, we conclude that the vortex motion above the
second peak is plastic when $j\to 0$ and there is no vortex glass phase at
finite temperatures in Bi-2212. The peak of S is then explained as the
crossover between different meta-stable vortex states.
