  We use a Monte Carlo bond-switching method to study systematically the
thermodynamic properties of a "continuous random network" model, the canonical
model for such amorphous systems as a-Si and a-SiO$_2$. Simulations show
first-order "melting" into an amorphous state, and clear evidence for a glass
transition in the supercooled liquid. The random-network model is also extended
to study heterogeneous structures, such as the interface between amorphous and
crystalline Si.
