The spectral representation of potential fields has gained a great deal of importance within the last decade. There have been two main categories of application. The first one relates to the interpretation of single anomalies, which are interpreted in terms of a single homogeneous body by means of certain characteristica of the spectra. Examples have been given by Odegard and Berg (1965), Sharma et al (1970), Sengupta (1974), Bhattacharyya (1966), Bhattacharyya and Leu (1975, 1977), Bhimasankaram et al (1977), Collins et al (1974). The second category relates to the interpretation of a whole collection of anomalies, which are interpreted on a statistical basis by extracting main features from the average spectra. Examples have been given by Spector and Grant (1970), Treitel et al (1971), Cassano and Rocca (1975), and Hahn et al (1976).