  We present further evidence for the bulk nature of the phase transition line
in the fundamental--adjoint action plane of SU(3) lattice gauge theory.
Computing the string tension and some glueball masses along the thermal phase
transition line of finite temperature systems with $N_t=4$, which was found to
join onto the bulk transition line at its endpoint, we find that the ratio
$\sqrt{\sigma} / T_c$ remains approximately constant. However, the mass of the
$0^{++}$ glueball decreases as the endpoint of the bulk transition line is
approached, while the other glueball masses appear unchanged. This is
consistent with the notion that the bulk transition line ends in a critical
endpoint with the continuum limit there being a $\phi^4$ theory with a
diverging correlation length only in the $0^{++}$ channel.
