<Tr> <Td> Granite </Td> <Td> 0 - 50 </Td> </Tr> <Tr> <Td> Rhyolite </Td> <Td> 0.2 - 35 </Td> </Tr> <Tr> <Td_colspan="2"> Metamorphic </Td> </Tr> <Tr> <Td> Gneiss </Td> <Td> 0.1 - 25 </Td> </Tr>

Who discovered the magnetic anomalies at ocean ridges