text: On polar reversal, read\nhttp://www.nasca.org.uk/Strange_relics_/reversal/reversal.html\nand\nhttp://www.nasca.org.uk/Strange_relics_/reversal/reversal_latest/reversal_latest.html\nand maybe also this\nhttp://pubs.usgs.gov/gip/dynamic/developing.html\n\nI heard about the melted rock and the Jurassic human campfire theory. But I believe it has been countered by the fact that (at that time) very small amounts of magma have been pushed up "gently and quietly" through a thin crust, and cooled there.