Travel Reference
In-Depth Information
tadiated outward to ever more distant localities. The first stop was Waldron
Island, largely uninhabited and composed of great walls of massive sedimen-
tary rock. On my first trip there I was struck by the difference in appearance
between the fossiliferous rocks of Waldron and those on nearby Sucia. The
Waldron rocks were much coarser-grained. This was evidence that they had
been deposited in shallower water than the rocks on Sucia. Many of the fos-
sils were different as well. There were far more clams and snails than on
Sucia and far fewer ammonites, two bits of evidence that also attested to an
origin in shallow water. The ammonites that were collected seemed to be-
long to species different from those on Sucia. But were the differences in fos-
sils due to differences in time or to the fact that the rock type was different?
Hete was another problem first discovered by the pioneering European geol-
ogists. Time was not the only variable that affected fossil content. Most ani-
mals are adapted to living in very specific environments. D'Orbigny was the
first to suspect differences in fossil content could sometimes be related to his
sampling different environments, not to a different time of origin. Time units
had to be independent of environment, but this is rarely the case, d'Orbigny
and others found. Such was my problem with Waldron Island.
Day after day I motored to this island and collected fossils from its
rocky cliffs. The work was wonderful: perfect temperatures, abundant wildlife,
no people. But the implications were troubling. As more and more fossils
came to light, I was faced with three choices. Waldron was older, Waldron
was younger, or Waldron was the same age as Sucia, but because its rocks had
been deposited in a different environment, its fossils were different as a result
of differences in ecology, not time. How to choose?
The answer to this riddle was supplied by William Gabb, whose work
was done a century before mine. He had collected a species of ammonite from
Chico Creek that turned out to be identical to those I found on Waldron Is-
land. This ammonite, at least in California, was known to be
older
than sev-
eral species of ammonites found both in California and on Sucia Island.
However, several other of the ammonite species that I collected from Wal-
dron Island were the same as those found on Sucia. Thanks to this particular
correlation, I was able to propose that Waldron was slightly older than Sucia.
