Ground magnetometer traverses over drift-covered Tertiary basalt areas in north- east Ireland have revealed large-amplitude anomalies (>2000nT). Fault zones produce characteristic wide-zoned, large-variance, high-frequency anomalies, while faults that juxtapose basalts with different magnetic properties, or basalt against a non-magnetic lithology, can be identified. Plugs and relict fissures both produce large magnetic anomalies (up to 4000nT). Dykes associated with the basalts generally give anomalies of <500nT, with the largest dykes giving a maximum anomaly of- 2000nT. This magnetic profiling technique can be used to identify and interpret geological structures present in the basalts in drift-covered areas with little or no