Near
Lexington, we have the joy of seeing the sun rise over the Blue Ridge Mountains
to the east and watching it set over the linear ridges of the Allegheny
Mountains to the west (click on the maps to get a larger view). These
mountains and their neighboring valleys hold a great diversity of rocks,
from the igneous rocks of the Blue Ridge to the fossil-bearing rocks of
the Shenandoah Valley, to the hard, sandstone ledges underlying the rapids
of Goshen Pass. In the rocks of Rockbridge County is
nearly the full history of the Appalachian Mountains. From volcanic
basalt telling of the early rifting of the Pangea continent some 650 million
years ago, through stacked sequences of limestone, shale, and sandstone
that illustrate the growth and subsequent consumption of the Iapetus Sea
to 350 million years ago. But the story doesn't end with the rocks.
The
topography that we see today in our valleys and mountains reflect the ongoing
battle between the uplift of rocks and their erosion by wind, water and
ice. We see rocks that were formed 10's of kilometers below the earth's
surface in the peaks of the Blue Ridge. These are testament to the
uplift of a Himalayan scale mountain chain that was leveled by the day-to-day
tearing down by erosion. This erosion continues today as the rocks of our
county pass out through the Blue Ridge in the James River to become new
rocks at the Atlantic shore.
We are going to focus on just two aspects of the geologic evolution
of the Appalachian orogen.
1. How Plate Tectonics
explains the uplift and deformation of rocks, and
2. The role of River Erosion
in tearing mountains down.
If you want to learn more about basic geology, here are some stops on
the WWW.
US Geological Survey Learning
Web
or their TerraWeb
or NASA
A good reference page for adult kids here.
created by Dave Harbor