When, about fifteen years ago, I along with many other new workers in the field of rock magnetism, started to read ourselves into the subject of continental drift, we found a complex, controversial and perplexing situation, with a very long history. In about 1620, Francis Bacon, in his search for regularities in nature, wrote: ‘...the very configuration of the world itself in its greater parts presents Conformable Instances which are not to be neglected. Take for example Africa and the region of Peru with the continent stretching to the Straits of Magellan, in each of which tracts there are similar isthmuses and similar promontories; which can hardly be by accident. Again, there is the Old and New W orld; both of which are broad and extended towards the north, narrow and pointed towards the south.’ Though Bacon thought the similarity of shape could not be by accident, he did not explicitly suggest that the two continents might have once been together. This hypothesis seems to have been first mentioned by von Humboldt about 1800: he also suggested a possible mechanism as to how the continents might have drifted apart: