Recent advances in rock magnetism have established the value of measuring the direction of the remanent magnetism of many kinds of rock. Provided certain conditions are satisfied, individual measurements relate to magnetic pole positions and sufficient measurements give a mean position which may indicate the geographical pole. Thus from determinations of a number of samples of rock from a geological formation, with suitable corrections, the latitude and geographical orientation of the rock at the time when it assumed its magnetic field may be postulated. This restricts and, in due course, may define palaeogeographical reconstructions and so serve to identify movements of the crust in relation to each other and to the poles. Results so far obtained show that averaged pole positions from successive rocks, ranging through many hundreds of millions of years in the same relatively undisturbed areas, lie on curves extending through many tens of degrees of arc. Moreover, similar curves, uniting near the present poles today but diverging considerably when traced backwards in time, derive from different continents, suggesting that both relative continental movements and polar wandering must be taken seriously. From the pattern of pole positions from dated rocks it may be possible to correlate rocks of unknown age (e.g. unfossiliferous and Pre-Cambrian rocks), and solve some petrogenetic problems.