The complex magnetic anomaly situated in the region of Reading and Newbury has been investigated using several techniques. Analysis of the power spectrum of the anomaly indicates that it results from two groups of sources: a shallow group at a maximum depth of some 1.1 km and a more extensive, deeper group at a depth in excess of 2.5 km. The anomalies due to these two sources have been separated by wavenumber filtering and continuation methods. The deeper group of sources appears to have a significant remanent magnetization and could be modelled by an approximately prismoidal body with a side length of some 20 km. The shallow group of sources appears to correlate with igneous rocks encountered in local boreholes. The magnetic properties of these rocks have been determined.