Travel Reference
In-Depth Information
The San Andreas fault and the trajectories of the two rock masses it
sepatates also provide an excellent model for envisioning
how
many conti-
nental margins interact. One of the great discoveries of the continental drift
model is that continents not only slide across the surface of the globe like
lugubrious bumper cars, alternately smashing into and fleeing other conti-
nental entities, but also
grow
through plate tectonic processes. Small slivers
of othet land masses—islands and pieces of other continents—these litho-
logical flotsam drift ashore and meld on the edges of larger continents
through the long eons of time. And in the process, they inexorably enlarge
various continental bodies.
North American is no exception to this steady continental enlarge-
ment. Starting as a central core of ancient rocks such as gneiss, gtanite, and
schist several billion years ago, North America grew as successive waves of
small lithic immigrants either accreted onto its coasts or became cemented
in place due to the collision of North America with some other continent.
Along the eastern seaboard of North America, the Appalachian Mountains
swelled upward and outward, first by mountain fotmation inland of active
subduction zones, later by the collision of North America with Europe and
Africa.
Mountains also grew in western North America, but differently than in
the east. Subduction took place, creating high volcanoes. But many more,
smaller pieces of drifting crust collided and became accreted onto our wan-
dering continent. Exactly how and
when
such smallet pieces accreted onto
the western coast of North America has been the source of enduring dispute.
A territorial dispute
Perhaps no block of this itinerant real estate has created so much contro-
versy as the region encompassing Vancouver Island and Western British Co-
lumbia. The conflict is ovet whether this giant region was formed through
the collision of one or more subcontinents smashing into the larger North
Ametica coast and thus is the first and still-enduring example of what is now
