Very few areas of the ocean basins have linear magnetic anomalies that are symmetrical with respect to midocean ridge crests. Indeed, asymmetry--not symmetry--is the rule. Although so-called linear anomalies characterize parts of many midocean ridges, they are absent from 12,500 km of the midocean ridges.

Dating of anomaly sources is restricted to the axial anomaly, and it is not certain that even the central anomaly really has been dated. Anomaly sources away from the axial anomaly have not been dated with certainty.

The anomaly bands strike into the continents in at least 15 places. Plotting of the linear anomalies demonstrates that they are approximately concentric with respect to Archean shields, and that they "dive" beneath Proterozoic and younger rocks of the continents. Therefore, geologic evidence indicates that the linear magnetic anomalies of the oceans are neither a product of igneous intrusions since Permian or Triassic time, nor a "taped record" of sea-floor spreading and earth magnetic field reversals during the past 200 m.y. Instead, the evidence suggests that the so-called linear magnetic anomalies are features which first formed during Archean time and which have been modified since.