  In this paper we examine the classical evolution of a cosmological model
derived from the low-energy tree-level limit of a generic string theory. The
action contains the metric, dilaton, central charge and an antisymmetric tensor
field. We show that with a homogeneous and isotropic metric, allowing spatial
curvature, there is a formal equivalence between this system and a scalar field
minimally coupled to Einstein gravity in a spatially flat metric. We refer to
this system as the shifted frame and using it we describe the full range of
cosmological evolution that this model can exhibit. We show that generic
solutions begin (or end) with a singularity. As the system approaches a
singularity the dilaton becomes becomes large and loop corrections will become
important.
