On: “Determination of crustal interface topography from potential fields” by M. Pilkington and D. J. Crossley (GEOPHYSICS, 51, 1277–1284, June 1986) and “Inversion of aeromagnetic data for multilayered models” by M. Pilkington and D. J. Crossley (GEOPHYSICS, 51, 2250–2254, December 1986).

The introduction of the airborne magnetometer in the 1940s led to the largest flow of data in geophysical history. Vacquier (1951) recognized the need for a concomitant system of interpretation of these data and pioneered the utilization of a rejected category of anomalies, the intrabasement contrasts in magnetization, for the basis of the desired system. These anomalies had great acclaim in oil and gas exploration in the late 1920s, but they led to the total disrepute of magnetics when facsimiles to the coincidence of production and intrabasement magnetization at Hobbs, New Mexico, discovered in 1928, did not achieve the same relationship. But Vacquier recognized the omnipresence of these anomalies, the singularity of individual anomalies, and their source in thick bodies of relatively steep sides and induced magnetizations. These simple but powerful deductions were reached pragmatically. To repeat, anomalies were singular because they were quite separate from one another. Therefore, the sides of their causative bodies had to be quite steep. An anomaly must be attributed to one magnetization contrast because it was one anomaly, and that magnetization was induced because the ratios of their positive and negative components correlated with the inclination of the Earth’s main magnetic field. (All of this may be found in GSA Memoir 47, 1951.)