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the same result. You might say the paleomagnetist has to cook the data. And
there is still more! Lots of rocks have no magnetite, or magnetite is present
in such vanishingly small quantity that the standard magnetometer cannot
detect the ancient magnetic field. In this case a new instrument must he em-
ployed, a superconducting instrument that has extremely high sensitivity.
Thankfully, the Chico Creek cores showed no such problems. Accord-
ing to my learned paleomagnetist colleagues, they "behaved" beautifully:
They had a strong signal, showed both normal and reversed polarity, and
seemed to have no overprint. With minimal laboratory effort we attained
publishable and very interesting results. We were able to identify the Creta-
ceous "long normal" and the first reversal above it. For the first time, rocks
from the west coast of North America could be reliably dated and correlated
with European stages and deep sea sediments. I was converted. This method
seemed too good to be true. You guessed it. It was.
Over the next two years, Jim Haggart and I scoured the eastern and
western sides of the Great Valley sequence, drilling rocks and collecting am-
monites. We helped tie the local California strata and its enclosed ammonite
biostratigraphy to the international time scale. There were no ashes for us to
date, so there was no way to find absolute ages. But the long normal polarity
followed by this first reversal was a time marker almost without peer in the
geological record. Soon after our confirmation of this reversal in Cretaceous
rocks of northern California, my colleague David Bottjer and others from
southern California located it as well. I was spoiled by this early success.
We seemed to be on the verge of a major breakthrough in telling time
in western North America. But the process was so convoluted! We needed
to compare the age of the rocks in California with those of the Vancouver Is-
land region and then compare both with the regions in Europe where the
various time units were first identified. These European "standards" of com-
parison are called stratotypes. We could do this if we could rind ammonite or
other fossil species that had lived in both places. But none had! We ourselves
could make the comparison if we could find rocks in both regions that could
be radiometrically dated with a mass spectroscope. But neither Europe nor
the Vancouver Island region had the necessary bentonites (ash layers) in-
