A little off-topic, but interesting: Chris Rowan writes about paleomagnetic reversals and crustal movements some billion years ago.
The change in inclinations through the section indicates that North America moved almost 30 degrees - around 3000 kilometres - southward in just 11 million years of volcanic activity. This means that the plate that it was located on was travelling at a speed somewhere between 20 and 40 centimetres a year, which is significantly faster even than India prior to its collision with Asia. Rather intriguingly, we may have replaced one geological mystery with another.
