Travel Reference
In-Depth Information
the landscape itself. The limestone is far harder than the shale and less eas-
ily eroded; because of this, the limestone makes up the ridges and high
places, and the softer shale is usually found at lower elevations. You can lit-
erally map the topography by mapping the limestone and shale, its locations
brought about by ancient changes in ancient sea level.
Worldwide units. It seemed the very essence of circularity. It took high-
precision, worldwide correlation through fossils and radiometric dating to
convince scientists that the fluctuations in sea level, as deduced from the
rocks left behind, were worldwide in scope. Yet once that had been proved,
the very changes in sea level—the worldwide sea level curve—became a new
sort of clock, a new way of telling time. Once you find your place in the sea
level curve, you can make powerful predictions about time.
It would seem that there could be no two places more dissimilar than
the green islands of the Vancouver Island region of North America and the
deserts of northern Africa. The rocks are equally dissimilar: the dark olive
sandstone and shale of the Nanaimo Group and the white limestone of
Tunisia. Even the fossils in both regions are different, and no species com-
mon to both exists. But they are united by their age: Both sets of rocks were
deposited between 80 and 65 million years ago, and being of the same age,
they experienced the same fluctuations in sea level. The simplest of all time
machines, detailed observation, has shown us that this is so and has eluci-
dated two ancient places and their environments.
