Travel Reference
In-Depth Information
It is much easier to tilt a rock than to transport it. Tilting takes place all
the time: just look at any range of mountains and you will find rocks in every
conceivable orientation, including turned upside down. The paleomagnetic
interpretations relied on the ability to recognize
original horizontally
of the
sampled rocks. This was a key argument leveled by critics of paleomagnetic
studies: The rocks sampled were not horizontal, and therefore the results
wete spurious.
Thus the controversy started, pitting "drifters," or those who believed
that the various tectonic pieces now making up the Western Cordillera had
assembled by continental drift, against "fixists," who believed that no such
assemblage of exotic terranes had taken place. The fixists did not doubt the
validity of continental drift; they just believed that many continental drift
theories as applied to the western United States and Canada were simply fig-
ments of overwrought geophysical imaginations. Besides, argued the fixists,
Mt. Stuart and the North Cascades are not located on the coast but are miles
inland. If they had been transported, then surely all rocks to the west of them
had to have been transported as well, and there was no apparent evidence of
that. Then, in 1977, a study defining and identifying the greatest suspect ter-
rane of all was published, and this significantly changed the debate.
A prime suspect
The definition of the giant exotic terrane known called
Wrangellia
(after the
Wrangell mountains of Alaska) was for several reasons a watershed event in
plate tectonic study. First, the study was published by three senior and highly
respected geologists employed by the United States Geologic Survey: David
Jones, Norm Silberling, and John Hillhouse. Second, until that time most
exotic terranes were hypothesized to be small land masses—island-sized at
best. The Wrangellia Terrane as first envisioned was enormous: a relatively
thin strip of land running north and south for many hundreds of kilometers.
Finally, the means used to identify this ancient land mass and its drift history
provided a methodological example fot most subsequent examinations of
