  We use a model of galaxy disk formation to explore the metallicities, dust
content, and neutral-gas mass density of damped Lyman-$\alpha$ (D\lya)
absorbers. We find that the [Zn/H] abundance measurements of D\lya systems now
available can be reproduced either by a population of low surface brightness
(LSB) galaxies forming at redshifts $z > 3$, whose chemical contents evolve
slowly with time and whose star formation rates are described by continuous
bursts, or by high surface brightness (HSB) galaxies which form continuously
over an interval of $z \sim 0.5-3$ (and no higher). Although, in reality, a
mixture of galaxy types may be responsible for low-z D\lya systems, our models
predict that HSB galaxies form more dust, more rapidly, than LSB galaxies, and
that HSB galaxies may therefore obscure background QSOs and not give rise to
D\lya lines, as suggested by other researchers. Significantly, we find that the
rate at which HSB disks consume neutral gas is too fast to explain the observed
evolution in the neutral gas mass density with redshift, and that the
consumption of hydrogen by LSB galaxies better fits the data. This further
suggests that LSB disks may dominate the D\lya population at high-redshift.
