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We have compiled a new and extensive catalog of heavy-element QSO absorptionline systems and analyzed the distribution of absorbers in bright and faintQSOs, to search for gravitational lensing of background QSOs by the matterassociated with the absorbers. There is a highly significant excess of C {\sciv} absorbers in bright QSOs in the redshift range $z=1.2-3.2$, and this excessincreases strongly as a function of QSO absolute magnitude. No significantexcess is found for Mg {\sc ii} absorbers in the redshift range $z=0.30-1.55$.We rule out several possible reasons for this effect and argue that the C {\sciv} excess could be due to gravitational lensing. If so, then the lensingmasses must be at $z \gtrsim 1.5$ and within several hundred comoving Mpc ofthe QSOs, where the C {\sc iv} absorbers are mainly found. The absence of anexcess in the available Mg {\sc ii} sample would then arise because the Mg {\scii} data does not sample this region of space.Comment: 21 LaTeX pages with 5 encapsulated Postscript figures included, uses  AASTeX (v. 4.0) available at ftp://ftp.aas.org/pubs/ , to appear in The  Astrophysical Journal, Sept. 20, 199

An Excess of C IV Absorbers in Luminous Quasars: Evidence for Gravitational Lensing?