  Using archival Far Ultraviolet Spectroscopic Explorer (FUSE) and Hubble Space
Telescope (HST) data, we have assembled a survey of eight sightlines through
high-velocity cloud Complex C. Abundances of the observed ion species vary
significantly for these sightlines, indicating that Complex C is not well
characterized by a single metallicity. Reliable metallicities based on [OI/HI]
range from 0.1-0.25 solar. Metallicities based on [SII/HI] range from 0.1-0.6
solar, but the trend of decreasing abundance with HI column density indicates
that photoionization corrections may affect the conversion to [S/H]. We present
models of the dependence of the ionization correction on HI column density;
these ionization corrections are significant when converting ion abundances to
elemental abundances for S, Si, and Fe. The measured abundances in this survey
indicate that parts of the cloud have a higher metallicity than previously
thought and that Complex C may represent a mixture of ``Galactic fountain'' gas
with infalling low-metallicity gas. We find that [S/O] and [Si/O] have a solar
ratio, suggesting little dust depletion. Further, the measured abundances
suggest an over-abundance of O, S, and Si relative to N and Fe. The enhancement
of these alpha-elements suggests that the bulk of the metals in Complex C were
produced by Type II supernovae and then removed from the star-forming region,
possibly via supernovae-driven winds or tidal stripping, before the ISM could
be enriched by N and Fe.
